Adds raycasting ability using bullet for RigidBodyManipulator.
Adds a test for raycasting.
 Merge branch 'collision-dynamics-integration' of github.com:andybarry/drake into collision-dynamics-integration.  This is a rebase from andres's branch to drake/master.
Merge branch 'collision-dynamics-integration' of github.com:andybarry/drake into collision-dynamics-integration