mdl skin loading is now more memory-efficient (now stores the original

mdl skin loading is now more memory-efficient (now stores the original
pixels and uploads textures on demand - many skins are never used, so
this saves some system memory)
added palette_featureflags[] for use by mdl skin loading
added TEXF_PRECACHE to all texture uploads that did not use it
added skinframe->hasalpha flag to clean up code
removed R_TextureHasAlpha function
r_glsl 1 no longer uploads fog textures
r_glsl 0, gl_combine 0 no longer loads gloss/normalmaps

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@9550 d7cf8633-e32d-0410-b094-e92efae38249