Restructure bm.c for merging
Set Texture* values at load time
Restructure bmread.c for merging
Add whitespace to fix rainbow parentheses
Only write player file if new highest level is higher than old
Move editor texture data into load_mine_data
Remove obsolete uvl processing

Descent refuses to load mines with version less than 16, so fixing up
uvl values in mines less than 15 is never used.