Fix Q2BSP texture loading, Q2BSP contents issues, and add support for SURF_ALPHATEST...

Fix Q2BSP texture loading, Q2BSP contents issues, and add support for SURF_ALPHATEST for any maps that might use it, force fullbright rendering on SURF_TRANS33/SURF_TRANS66/SURF_WARP textures which fixes the rain in 3v3gloom3.bsp and chainlink fence textures on tkse.bsp and glass transparency on gloom1se.bsp among others.  Also fix the SURF_FLOWING scroll rate when combined with SURF_WARP.

Also fixed the collision issues caused by stomping over Q1BSP data which caused traceline to break on Q1BSP after loading a Q2BSP map, thanks Supa for that bug report and finding other Q2BSP issues.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12284 d7cf8633-e32d-0410-b094-e92efae38249