detail texturing added (although with just one generated texture applied to everything)

detail texturing added (although with just one generated texture applied to everything)
detail texturing makes use of up to 3 texture units if you have combine
detail texturing added to effects options menu (r_detailtextures cvar)
surfvertex_t now has another set of texcoords, for detail texturing
Mod_BrushStartup and Mod_BrushShutdown functions added to alloc/free the detail texture
r_multitexture cvar renamed to r_textureunits, so you can limit number of texture units enabled for testing, rather than just as a yes/no kind of option
gl_combine is forced to 0 if r_textureunits is less than 2 (this is purely for consistency, not of any importance)
split up the wall rendering into two kinds - vertex lit with optional transparency, and opaque lightmapped with no support for transparency
R_Mesh_Draw_GetBuffer now takes a wantoverbrights parameter, if false it will not use the 4x overbright (even if combine is enabled), this is useful to improve the color precision of anything which does not need overbright
fixed crosshair brightness (it was unintentionally adjusting the alpha using m.colorscale just like the RGB portion of the color)
sprites only use overbright if they are lit (normal unlit sprites are rendered without overbright)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@2282 d7cf8633-e32d-0410-b094-e92efae38249