spearmint: Fix polybuffers!

The wrong entitynum was used making not draw in the correct place!
Also fix RB_SurfacePolyBuffer to append to current draw surface instead of overwritting.
spearmint: Increase max polys, polyverts, and polybuffers

Change max polys and polyverts to RTCW/ET values.
Change max polybuffers from 128 to 1024. (ET's max is 4096.)