Demo replay fixes

Changes made/bugs fixed in this branch:
* Replay camera is now controllable when climbing (https://mb.srb2.org/showthread.php?t=38668), and in waterslides
* localangle (read: the angle between you and the camera, I think) now doesn't change during demo replays in most situations, unless the player is in analog mode. Exceptions include zoomtubes and NiGHTS super
* Replay camera now doesn't act silly if the player is in analog mode (assuming you also recorded it in that mode to begin with, anyway)

See merge request !66

Fix F12ing an analog player changing cam_rotate

I didn't test this but it looks like it would work. Idk.

See merge request !70

They don't affect what you're viewing anyway and cause cam_rotate to get
messed up.

DO NOT MERGE THIS INTO THE INTERNAL REPO. This is a temporary 2.1.15 only fix. This commit allows an optional boolean for tan(), which when true will automatically shift angles by ANGLE_90.

Multiply downwards thrust on slopes by the actual "gravity" variable. Also account for mobj scale (it affects gravity added in P_CheckGravity, so it makes sense here).

the most common condition (correct drawing) shouldn't be last, however it can't be first without making the conditions longer anyway.

it's a nitpicky thing, but this is the renderer we're talking about here.

i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs i hate FOFs

Previous overflow fix resulted in extra tall FOFs disappearing up close (see: ERZ1's elevators at start)
This works "better" in that only some lighting bugs and really really finicky visual glitches show now. I give up trying to totally fix this stuff dfsdfgdgf

One more name in the credits

I probably messed up by making toast_credits based on master instead of next. If that's blocking, just delete this branch and I'll re-do it. It's a single line, though - shouldn't exactly matter so much.

Could probably stand to be merged into Internal as well, since I hadn't actually worked on any textures when we'd updated the credits there.

See merge request !69

please don't make me do this again.

see https://mb.srb2.org/showthread.php?t=41370

OpenGL slopes

Exactly what it says on the tin, obviously.

See merge request !68

Revert "Fix up the ceiling sky hack (yuck) a bit so my commit doesn't break thok barrier planes now"

This created HOMs in THZ2's skybox, ack.

This reverts commit eba382df.

Interestingly these changes somehow fix how thok barrier walls block the planes, which was an issue even before slopes I believe

that is, I believe slopes are why he added this code anyway *shrugs*

This fixes the annoying flickering when you pass by water, FOFs, tall grass, etc.

This breaks plane display for thok barriers

This reverts commit ee00da6a.

Fix portal and plane/sky interaction

More portal-related fixes:
* Fixes rendering issue 4 from issue #21 (Slope planes render with wrong height values when visportals are visible on-screen)
* Fixes sky rendering through portals, so that the sky you see through each portal is what you'd expect to see if you were actually there. Easiest way to see what I mean is through sky 22's planet, in a map with portals at 90 degrees to the other sides respectively (the example map on the wiki for ld40, for instance).

See merge request !65

The idea is for the layman Lua user to understand better what range of values to use for mobj types, states, sfxs, player #s etc. Additionally, mobjinfo/states/sfxinfo/hudinfo tables all now have actual bound checks when accessing/editing them. Yikes, why didn't they have any before?!

Should fix conflicts with Lua-scripted jump spin abilities.

Fix OpenGL Fademasks (Screen Transitions)

Screen transitions don't work in OpenGL when scr_depth is set to 8 or 16 bits.
This fixes that.

See merge request !67

For some reason every texture and flat loaded into GL is vertically flipped

Fixes http://mb.srb2.org/showthread.php?t=41403. Not sure why nobody noticed this earlier.

Don't think either of them need RGBA

So they don't get effected by the texture format set by the screen depth
GL_RGB5_A1 from 16-bit was removing all alpha from the texture