fixed a flaw in Mod_Q1BSP_RecursiveRecalcNodeBBox, it was merging bounding boxes...

fixed a flaw in Mod_Q1BSP_RecursiveRecalcNodeBBox, it was merging bounding boxes even if they came from solid leafs, which meant that the solid hull around the world was making almost all nodes have a bounding box of +-1 billion units, negating any benefit at all to node bounding boxes
10% speed gain in masque.bsp by changing pvs box checking functions to use box tests when recursing the bsp tree instead of BoxOnPlaneSide (now that the node boxes are usable)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@5764 d7cf8633-e32d-0410-b094-e92efae38249