Make kamikaze timer loops use level.num_entities instead of MAX_GENTITIES

Optimization. Many other loops use level.num_entities, there was no
special reason that MAX_GENTITIES was used for these.
Merge remote-tracking branch 'ioquake3/master'
Rewrite commercial pk3 detection, include q3/ta demos, rtcw, et

Detect pk3s by checksum to be faster, but still confirm gamedir/filename to avoid false positives.
Check for commercial pk3s once at runtime instead of each time downloads are initiated.
Remove special handling for Q3 and Team Arena fs_game

Team Arena now require spearmint-patch-data in order to run.