Collisions between bots?
Should be in the physics module. If you're going to look at 2.37's collision routines, prepare to be confused, because there's alot going on that can boggle your mind if you're not familiar with physics and math and programming...
2.4's collision routines are more compact and understandable, but weaker. Bots can overlap for a number of turns in 2.4, whereas they couldn't do that in 2.37.