This cleans up texture_t and possibly even improves locality of
reference when running through texture chains (not profiled, and not
actually the goal).
r_screen because of SCR_UpdateScreen, and r_cvar because the cvars
really should never have been in a plugin in the first place (and
r_screen needed access).
This allows the vid module to load the render module and access render
specific functions before the renderer initializes, which happens to need
an initialized vid module...
The renderer now gets initialized and things sort of work (qw-client will
idle, though nothing is displayed). However, as the viddef stuff is broken,
it segs on trying to run the overkill demo.
Still, nothing will work: no plugins are loaded and they're all broken
anyway.
glx, sgl, glslx etc are going away, just the basics will be built: fbdev
(probably go away eventually), sdl, x11 and hopefully someday win. That's
actually the only reason anything links.
