- use VM_* macros for bmpman since it didn't seem to register the memory correctly (temporary)
- a little "stupid" fix for dds bitmap reading
- fix it so that memory is released properly on bitmap read errors
- some cleanup to model texture loading
- allow model textures to get released rather than just unloaded, saves bitmap slots
- bump MAX_BITMAPS to 4750, should be able to decrease after public testing of new code