added mleaf_t->containscollisionsurfaces variable which indicates if the leafsurfaces...

added mleaf_t->containscollisionsurfaces variable which indicates if the leafsurfaces array contains any q3 patches to collide against, checking this saves a substantial amount of time on collision detection in q3bsp (as few leafs actually contain patches, but many contain other kinds of surfaces)
added combinedsupercontents variable to mnode_t and mleaf_t, this was intended for collision culling but is not actually used (checks are implemented but commented out, because there was no measurable speed increase, and it could cause inconsistent results for startcontents when tracing objects larger than a point test - since point tests are always about contents there is no such culling performed in that case)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@6878 d7cf8633-e32d-0410-b094-e92efae38249