protection against bad avatar-avatar collisions

Also with logging if we encounter incorrectly large penetration depths
check for bad deltaTime during avatar-avatar collisions
fix #2656 avatar jumps very far away

This was caused by a bad CapsuleShape::_radius when the default
CapsuleShape was used to create a default bounding capsule.  The
penetration against such a shape could be arbitrarily large.
merge upstream/master -> andrew/avatar-interaction
merge
merge
Merge pull request #2651 from AndrewMeadows/avatar-interaction

protection against bad avatar-avatar collisions