This port was started by Baker and finished by me (MH).

Most of the credit goes to him; I just fixed some bugs.

There are some that remain, not sure if they're inherited from the original zQuake or are new from the D3D8
wrapper :-(

- gl_texturemode always seems to start up as GL_NEAREST.
- The engine is SLOW.  Previous ports push 100 FPS on my machine, this one is lucky to get 50.  (For ref, GLQuake
  gets about mid 40s and DirectQ does about 125 on the same hardware).

I'm not going to fix these as I prefer to leave the original code as close to how it was released by the author
as possible.

One bug that was *definitely* from the original zQuake was relating to the solidskytexture always getting set
to 0 (no texture); this came from the external sky texture loader where - yes - solidskytexture is set to 0 if
no external sky texture is found.  I just cached the original value coming in and restored it going back out.

That one is marked "mh" in the code; I *did* feel it appropriate to fix.