Add sensor physics type.
A sensor can collision with any other objects, including other sensors
but does not restitue any force. Collision is controlled by a new
setting: collision mask. A sensor collides with another object
if the object group is part of the its mask.
Add 2 param to rigidbody_world.convex_sweep_test:
col_groups to indicate which groups we want to test
use_sensor to indicate if we want to detect sensor objects (default no)
return is a 5-uple, last value=reference to object hit (only if 4th
value=1)
new RB_dworld_get_collision_paris() to report the collisions that occurred
in last frame.
bug fix: ignore self object in convex_sweep_test.
make boolean parameters boolean
create ListBase for RigidBodyWorld collision pairs and RNA

@ben2620 check the notes in
rna_rigidbody_collision_pairs_begin
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.
Skip function for Collision Pairs

Make sure the pass works even if the objects are removed middle way through the
interaction
make sure collision_pairs is initialized as NULL
Fix segfault in convex_sweep_test when the object has no physics shape
Frame range of rigid body simulation is automatically adapted from scene
range.