Fix a bunch of compiler warnings. Also fix a peculiar bug in WriteBSP where EmitAreaPortals was called for each BSP submodel. Now we only call it once, in EndBSPFile.
Re-introduce use of vertex hash, which was accidentally dropped years ago. This not only fixes a compiler warning about unused variables *g*, it also brings BSP compile times down by 60%. Jester's big-ass map just went from 47s BSP time to 19s BSP time on my Macbook.
Another shot at build script cleanup.