made the Sorted Edge Rasterizer (hidden surface removal) optional as the r_ser cvar...

made the Sorted Edge Rasterizer (hidden surface removal) optional as the r_ser cvar, can be a speed difference
added back the old portal-passage worldnode code (sometimes faster)
recalculate node bounding boxes when loading (based on leaf bounding boxes which are calculated from portal generation)
added untested code for qftol (much faster double to integer conversion on x86, not used yet)
added a couple Hunk_Check calls while loading things (just to be a little more paranoid)
minor whitespace cleanup, some commented out code removed

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@956 d7cf8633-e32d-0410-b094-e92efae38249