Mex for geometricJacobian and findKinematicPath

* Wrote a mex version of geometricJacobian (and findKinematicPath, which geometricJacobian uses), so that we can use it for task space control on Atlas. 
* Moved tests that were in examples/Atlas to a better place, and updated them so that they compare Matlab vs. mex.
* geometricJacobian in C++ currently uses drakeJoints, so I'm conditionally compiling on Windows. However, the mex version is used by default if use_mex is not passed into geometricJacobians, so the test will fail. I don't want to check for existence of a mex file in Matlab geometricJacobian though, for performance reasons. Of course, really I need to get drakeJoint stuff to compile under Windows, but what do you think is the best solution for tomorrow?
* note that the floatingBase implementation of geometricJacobian will rely on a different format of kinsol, so I'll have to rewrite it later. Still, the findKinematicPath function will be useful later as well.
What does the `<memory>` library give us? Is that needed to define `nullptr`?