Add BKE_rigidbody_update_collision_pairs()

This function loads the list of collision pairs from bullet. Should
be called after a simulation step. Beware that simulation pointcache
does not store the collision pairs. Hence this list is not updated
if you change the frame number backward and load the object position
from the cache.
It is best to force a cache clean first to make sure that the rigidbody
simulation is executed.