OpenGL slope FOF lighting fix
This fixes some issues with sloped FOFs that affect lighting in OpenGL (as in, those that cast a shadow or have a colormap). Particularly, they can do strange things to any wall textures adjacent to them, as we've noticed ourselves in levels for 2.2. =P
See merge request !194
Polyobject seg render fix
This fixes both Software and OpenGL renderers so that polyobject segs aren't drawn if the game is drawing the actual subsectors they're from (outside the main level, where the polyobject walls were pre-spawn). They should only appear as part of the polyobject itself in-level.
This means a few glitches with polyobjects are probably fixed: for instance in Software mode, polyobject walls sometimes appear through level boundaries (and make everything above/below vanish, turning into HOM or skybox), if the BSP rendering code happens to find one of the subsectors said segs came from outside the level. I don't think anything similar happens in OpenGL, though I'm sure some unwanted typecasting is happening as a result of attempting to draw the segs. (And it fixes a crash in 2.2 anyway.)
See merge request !195
Polyobject segs should ONLY be drawn if the polyobject itself is in the polylist of a subsector being rendered. That way you won't sometimes see polyobject walls through level boundaries, if you happen to be close enough to their pre-spawn locations outside the level (or in them, if you decided to go on a noclip journey).
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
I added similar checks for the other num* but it seems some MD2s break the other limits without knowing anyway ...so I've commented these checks out for now, unless we have further discussion regarding them later on
* NAMEcL refers to a frame which is seen for the entirety of an object's left side.
* NAMEcR refers to a name which is seen for the entirety of an object's right side.
* NAMEcLcR does both sides.
* Having just a NAMEcL requires you to fill in the opposite side either with NAMEcn where n is 1 and 5 to 8 OR fill in with a NAMEcR
* Switches down the centerline of the object instead of at the ANGLE_202h interval for normal sprites.
* Characters were selected for 1) ease of use and 2) not getting in the way of adding support for zdoom's totally bananas 16-way sprite system at a later date if we so choose
