Some slope improvements/fixes (plus P_GetMobjGravity)

Dear Red, I did some things.

* Made the slope flag SL_NOPHYSICS actually have an effect like we wanted to, but didn't get around to implementing yet - activated by setting the slope's linedef flags to have ML_NOSONIC.
* Made downhill slope thrusts proportional to an object's gravity and friction.
* To make the above happen - seperated out the gravity value finding code in P_CheckGravity into a seperate function, P_GetMobjGravity. (p_mobj.c, p_local.h) I also made this function available to Lua.
* Turned those PANIC n console messages (which would inevitably be followed up with a crash, since we're accessing invalid memory immediately after) into a descriptive I_Error.
* Put the SRB2CB type-shimming behind an ESLOPE_TYPESHIM ifdef.
* Removed SPRINGCLEAN-ifdef'd code.
* Cleaned up some eosteric comments.
* NEW SINCE RED +1'd THIS: The teetering code now takes slopes into account pretty well. There are edge circumstances as outlined in commit 9d221f4f, but this is unilaterally better behaviour in every way and the teetering code was kind of a mess anyways.
* NEW SINCE RED AND ALAM +1'd THIS: P_ReverseQuantiseMomentumToSlope. Simple function that replaces the inverse angle stuff (which also wasn't using InvAngle, just ANGLE_MAX - angle - which is inaccurate!!)

Current testing files available at /toaster/slptst3.wad and /toaster/gravitytest.lua on the ftp.

I want to do more to the branch like implement SL_ANCHORVERTEX in the near future, but this is probably safe to merge in its current state.

See merge request !77

Climbing on one-sided linedefs

Does what it says on the tin. You couldn't before, now you can.

With this branch, thok barriers are now completely optional for maps with no aesthetic need for sky-topped walls. All the bugs and complications that exist with climbing right now still exist, except now there's one less issue making them suck forever and now Nev3r will be very happy.

Do I need a testing .wad? It's... not that hard to create a very small map and go nuts with Knuckles in it. I have one, but uploading it to the ftp almost feels insulting.

See merge request !90

The whole thing needs a refactor in general, but it's almost 2am here, I need my sleeb, and this fix would probably break something with 2.1 climbing if I made it any more/less (depending on viewpoint) complicated.

...completely misunderstood the reasons we weren't merging toast_slopes, mom holy fuck i'm stupid and bad

Enjoy your slopes without physics, people :D

# Conflicts:
#	src/p_user.c

Revert "Changed teetering to match the discoveries made about it in the sectorlist_traversal branch in a way that matches my revamps here, since I DID change a lot."

This reverts commit 19b186e5.

This reverts commit 1723bb55.

Sectorlist traversal

MOM GET THE CAMERA

There's a LOT of code in the source that ended up mixing m_snext (the node for the next thing in the sector's thinglist) and m_tnext (the node for the next sector in the thing's sectorlist), so I renamed the following:

* m_snext ==> m_thinglist_next
* m_sprev ==> m_thinglist_prev
* m_tnext ==> m_sectorlist_next
* m_tprev ==> m_sectorlist_prev

Then, I changed all the instances where the code was trying to go m_thinglist_next on a mobj's touching_sectorlist (which would've just gone to the node for the next thing in the same sector, instead of the node for the next sector for the same thing). Notable samples:

* FF_SHATTER blocks now disappear the moment you go into their sector. You still can't give FF_SOLID to them because in that case they will still stop you if you never enter their sector at all (ie - clip on corners), but having them nonsolid no longer allows you to phase through entirely without busting them (which was the whole downside of making them intangible in the first place).
* You can now bump into multiple Mario blocks at a time, even if you're not exclusively in their sector.
* No more getting randomly stopped on the edges of bouncy FOFs.
* Landing on polyobjects might behave a little more consistently at the edge of their host sector.
* Teetering did a SHITTON of code that basically never got executed, and then had directly-blockmap-accessing code as a backup. The code was activatable by replacing the m_thinglist_next with m_sectorlist_next, but it behaved SUPER differently from what we're used to with teetering (if the player mobj's edge was JUST off the edge of a platform, you ended up in teetering frames - even if it looked like you could stand) so I ended up removing that section entirely.

Any objections?

See merge request !85

Some other software fixes/changes

Some other software fixes/changes I've made

* Change 1: single-sided linedef midtextures (read: not double-sided linedefs, but single-sided) now don't skew if Effect 2 is checked. Before, there wasn't any ability for software to disable skewing for them. =V
* Change 2: PolyObject back side midtextures now return to being where they should be. Had to make a hack to fix this though.

See merge request !86

Fixes and changes related to the act of setting up a level (in other words, setup fixes)

Changes made in this branch so far:
* a REJECT lump of zero length (NOT to be confused with a REJECT lump of non-zero length with all-zeros, just to clarify) should no longer cause problems with netgames and otherwise. The game now checks if the lump exists, has the right name, and length is not zero - if it fails any of these, the REJECT lump is not loaded and P_CheckSight won't be allowed to use it. This means ZDBSP (no reject) should be safe(r) to use now!
* there's now a simple devmode-only message (requires "Setup" mode) if a sector is found to have no lines at all during setup. It's a far cry from the plot to I_Error the game I once had for that unsusal scenario, but such a level still works anyway so whatever.

See merge request !87

FF_REVERSEPLATFORM clipping

Ran into an issue whilst testing out one last feature (there's always one more...) for flat_alignment_revamp. This is a backported fix.

The bug was such that if you're falling through a platform with FF_REVERSEPLATFORM and not FF_PLATFORM, you'll be pushed downwards such that your head is against the bottom of the FOF. This just checks momz is greater than zero if it has FF_REVERSEPLATFORM to make sure it's okay to set ceilingz. (OR the alternative in reverse gravity.)

No test map because this was originally done for internal. Instead, test it on the other branch's test map.

See merge request !83

Software crashes fix

This branch SHOULD fix the many crashes people have reported lately that all point to the software renderer. Simply put, the software renderer allowed stuff to be drawn out of the screen even though that wasn't safe, and even the existing checks to prevent that didn't work.

If you saw me worrying about the sky HOMs I discovered in AGZ earlier in the commits for this branch, don't worry - it turns out that issue already existed in 2.1.15's srb2win.exe (and probably srb2dd.exe too) anyway, the changes in this branch didn't cause them. Hopefully nothing else broke then.

See merge request !75

P_ReverseQuantiseMomentumToSlope is now a function. (I was thinking about a macro, but couldn't get it down.)

Also, the teetering angle on slopes is now FRACUNIT/2 because there's literally no way to stand still on a slope that steep unless it doesn't have physics.

Effect 2 (No Midtexture Skew) now toggles off skewing for midtextures on single-sided lines, which was what was intended for them to begin with apparently.

This means the current skewing-by-default effect isn't changed, and OpenGL's equivalent code doesn't have to be touched since apparently it was already like that.

Added P_LoadReject function to properly check if REJECT lump is valid or not when loading it, so P_CheckSight can avoid accessing it if not.

This should mean that maps built with ZBSDP (no reject) should have less or no problems in netgames compared to the standard ZenNode maps now, hopefully. =)

note: once this is merged into internal, you should probably remove me from "programming assistance" so i'm not duplicated for no clear reason. unless you want me to slowly take over every section in the credits >:3c

"frontsector" in this part of the code isn't actually the polyobject's sector for back-side polyobject segs, it's the in-level sector the polyobject as a whole is being rendered in it turns out.

Red apparently left in code for single-sided linedefs to NOT skew their midtextures ...but it doesn't work because it doesn't stop the skewing code from running instead, regardless of whether Effect 1 is on or not. If it's decided single-sided line midtextures shouldn't do this though, the non-skew code could just as well be thrown out lol (or something else I guess?)

When I first wrote this, I thought the .h file that contained a function declaration needed to have the same name as the .c file the function was in. Now I know that's not the case, off to p_local.h with you.

Changed teetering to match the discoveries made about it in the sectorlist_traversal branch in a way that matches my revamps here, since I DID change a lot.

Two interesting points of note:
* The touchspecial sector flag seems to actually do its job now.
* Detection of sectors with polyobjects in seems to have done this incorrectly, but this doesn't mess with anything about touching the polies themselves so it seems to really only handle edge cases where the polyobject was too close to the border of another sector (which would've likely made rendering glitches anyways).
* There was a whole swathe of teetering code that was basically never run properly because of this mistake. I did a simple fix at first, but you started teetering whenever you were slightly less than your radius away from a sector's edge, which was completely different and undesirable behaviour. Instead, I cut out the code that was never running, and just left the hacky method in instead since it was more accurate to what we want in general.

Renamed some struct variables so the problem this branch sets out to fix is more obvious at a glance.

* m_snext ==> m_thinglist_next
* m_sprev ==> m_thinglist_prev
* m_tnext ==> m_sectorlist_next
* m_tprev ==> m_sectorlist_prev