Savegame hotfixes

Yes, this another netgame related fix! Named this "savegame hotfixes" rather than "ERCZ hotfix" or the like in advance of the fact we probably need a general branch for other $$$.sav fixes?

Anyway, fixes included in by this branch:
* ERCZ's lava falls now act as expected rather than being stuck in place for the map's duration, fixing all other known desynchronisation issues known in the map for the time being (yay)
* Changing sector tags in a map no longer causes joiners to netgames to have their SRB2 application stop responding etc
* Player names should no longer turn red in the console in gametypes outside of CTF/Team Match if a resynch occurs (not $$$.sav related, but it's related to netplay so I lumped it in anyway)

See merge request !150

Eggshield laser fix

Fix for http://mb.srb2.org/showthread.php?t=42250

See merge request !152

Fix egg guard shields being endlessly killed by lasers. Simply make sure they have health first before killing them!

One Eggscalibur fix

Use mobj->watertop instead of mobj->spawnpoint->z. CEZ3 is far from fixed in multiplayer, but this is still one less thing to worry about.

See merge request !148

Software plane rendering fixes/cleanup

This is mostly cleanup, with the exception that polyobject planes should now behave somewhat better than they do in 2.1 currently (translucent polyobj planes should now always be actually translucent regardless of where you view them from, for instance). I can't claim I've fixed their rendering once and for all though, there may still be bugs for all I know...

See merge request !136

Some texture-related fixes

Bugs fixed in this branch:
* upper/lower/middle textures with non-existent texture ids being capable of crashing the game. For instance, RVZ1 has colormap codes on non-colormap linedefs, which causes them to wind up with invalid texture ids because of how the game tries to interpret lower/upper textures with "#" followed by characters on normal linedefs. Fortunately these "textures" are normally not visible anyway (since they're all in control sectors) unless they are swapped with in-level textures by some crazy Lua script of some sort...
* animated single-patch textures with holes displaying garbage on first viewing (see this thread: https://mb.srb2.org/showthread.php?t=42195)
* the heights of the lighting (shadows or colormapping) from water/translucent/shadowcasting/etc FOFs become messed up when displayed on repeated midtextures.

See merge request !144

Flat changing hotfix

This should fix how Lua scripts that change flats in levels, particularly to flats that don't already exist in the level, cause SRB2 to crash for anyone who joins a netgame afterwards. (I'm not sure if it's a consistent thing or not though)

Probably needs a good test to verify the issue is completely fixed before being merged in. Maybe there are other minor things I didn't account for in this fix? I don't know!

See merge request !141

Fix player colors mysteriously turning red if a resynch occurs outside of CTF/Team Match. Not technically a $$$.sav fix, but still netplay related of course

At least, I assume this is how it's happening for some, I haven't been able to get the full info since WHERE IS EVERYBODY?

Dunno who thought it was a good idea to lump tag, nexttag and firsttag together in $$$.sav, but that meant changing sector tags caused SRB2 to stop responding since it lead to the tag lists being broken

This fixes ERCZ's lava falls not moving after joining a netgame at that stage. Possibly explains other various floor/ceiling related netgame quirks that haven't been noticed until now, maybe even in multiplayer levels.

Remove secplanes

This is just removing SSNTails's old port of ZDoom's secplane code and math, from back when he attempted slopes himself. The slopes we've had since 2.1.15 however do not need these, so we can pretty much toss the code for them out now (nothing uses them anyway).

See merge request !149

Netcode shit

Remove all traces of SSN's old port of ZDoom's secplanes for slopes, since our slopes do not need them

CEZ3 STILL has some ridiculous inconsistencies, but this is one less to worry about.

FixedRounding hotfix

Fix the FixedFloor, FixedTrunc, FixedCeil, and FixedRound functions.

See merge request !142

Savegame hotfix

This fixes the first mobj thinker added/read from $$$.sav not being relinked to other objects as their target/tracer/etc properly. In particular, this fixes Brak's electric shield disappearing for anyone joining a netgame playing ERCZ (as Brak happens to be the first object added/read in this case, and Brak is the shield's target).

See merge request !146

-Fixed broken net commands, thus fixing (or at least greatly improving) chat/commands/joins/leaves and possibly other annoying bugs
-Updated packet name list so the debug file no longer shows garbage packet names
-Replaced byte values with actual net command names in the debug file. Only the first net command in a packet will be shown though
-Added a MOBJCONSISTANCY define that makes the game takes all revelant mobjs to be counted in the synch seed
-Added a PACKETDROP define that adds two console commands "drop" and "droprate" to simulate bad internet by dropping packets
-Added/changed comments here in there in the netcode
-Fixed a minor error that would ignore one of the urgent ack slots
-Added a space between the map name and "zone" for the messages shown in a joiner's console

Start mobjnums at 1 instead of 0, so that the first found mobj can be relinked as a target etc to other mobjs properly

This fixes Brak's electric barrier disappearing for joiners to ERZC. There seems to be some issues with the lava falls there too I've found, but the electric barrier actually stays around now at least

(Fixes LSHIFT typing D repeatedly into chat)

Hook optimisation

Zlib pkgconfig

Linux build to include libgme by default

See merge request !116

Created R_CheckTextureCache to make sure midtexture/FOF walls cache their textures before choosing colfunc_2s, for software mode

Created R_GetTextureNum to make sure top/bottom/midtexture texture ids are always valid in rendering code for both software and OpenGL (and also for the Solid Midtexture effect physics code)

Generic mobj hooks are now run before mobjtype-specific mobj hooks, and player/linedef executor hooks now have their own lists

readme.txt duplicated, also incorrect

readme.txt should be README.md

No switching skins mid-credits/custom cutscene in SP

Does what it says on the tin.

See merge request !129

Smoother ropes and zoom tubes

Makes rope hangs and zoom tubes suck less. Specifically, they handle corners (and vertical height changes, ala sloped rope hangs) a LOT nicer. Ported from internal.

See merge request !139