lcp cache is a shared data handle (so it can be used between calls)
minor cleanup
Merge branch 'handsim' of https://github.com/RussTedrake/drake into handsim

Conflicts:
	systems/plants/TimeSteppingRigidBodyManipulator.m
resolves #512
handle empty active set
Hand mounted to robot, but pathlcp cries
Merge branch 'handsim' of https://github.com/RussTedrake/drake into gizatt_handsim
Plumbing for mounting hand to Atlas

Fixed bug in TSRBM that was unpacking / repacking x <-> q;qd
incorrectly; Atlas can now do previous tests with hands attached
in simul. Moving demonstrative code over to a new test, which will
get developed / cleaned up next.