If there were lots of selected objects without an existing rigid body,
we would add rigid bodies to them one by one.
This would be slow in python, now we instead do this as a batch
operation in C.
On my (Intel) MacBook it used to take 60 seconds and with this change it
takes about 0.3 seconds.
Reviewed By: Sebastian Parborg
Differential Revision: http://developer.blender.org/D11957
26b2a35dd4