Sync interface of BulletRobot with DynamicsRobot.

In general shared_ptr should be passed as const shared_ptr<>& as
outlined here:
http://herbsutter.com/2013/06/05/gotw-91-solution-smart-pointer-parameters/

git-svn-id: http://svn.code.sf.net/p/simox/code/trunk@704 042f3d55-54a8-47e9-b7fb-15903f145c44