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
Dunno who thought it was a good idea to lump tag, nexttag and firsttag together in $$$.sav, but that meant changing sector tags caused SRB2 to stop responding since it lead to the tag lists being broken
This fixes ERCZ's lava falls not moving after joining a netgame at that stage. Possibly explains other various floor/ceiling related netgame quirks that haven't been noticed until now, maybe even in multiplayer levels.
Remove secplanes
This is just removing SSNTails's old port of ZDoom's secplane code and math, from back when he attempted slopes himself. The slopes we've had since 2.1.15 however do not need these, so we can pretty much toss the code for them out now (nothing uses them anyway).
See merge request !149
Savegame hotfix
This fixes the first mobj thinker added/read from $$$.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
-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
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
