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).
It turns out glsl, sw and sw32 weren't getting any benefit from R_CullBox
because the frustum wasn't setup :P. Get another 8% out of bigass1
(174->184fps). bigass1 now runs 2x as fast as it did before I started this
optimisation run :)
Where possible, symbols have been made static, prefixed with gl_/GL_ or
moved into the code shared by all renderers. This will make doing plugins
easier but done now for link testing.
Also some small cleanups in particles.
Brighten grenade smoke a tiny bit, so it's not so invisible in the typically dark quake areas.
And some minor cleanups to water rendering.
