Added Draw_GetPicWidth, Draw_GetPicHeight, Draw_IsPicLoaded functions and moved cache...

Added Draw_GetPicWidth, Draw_GetPicHeight, Draw_IsPicLoaded functions and moved cachepic_t to live in gl_draw.c (no longer visible to other modules).

Changed Draw_CachePic to use the R_SkinFrame_LoadExternal system, and reworked font loading to use Draw_CachePic rather than keeping track of textures itself.  R_SkinFrame_LoadExternal can now load gfx.wad lumps and gfx/*.lmp files, and the embedded images have been moved to image.c as they are now returned as raw images, suitable for R_SkinFrame_LoadExternal to use.

Reworked cl_video code to not need the cl_dyntexture system (which has been removed); it still uses dynamic texture callbacks (which is a feature of rtexture_t).

Changed the parameters to Mod_LoadCustomMaterial and a few other model_shared.c functions to not assume loadmodel is the owner of memory and textures; this was necessary for Draw_CachePic to be able to use R_SkinFrame_LoadExternal.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12385 d7cf8633-e32d-0410-b094-e92efae38249