Add second derivatives to drakeFunction.Kinematic.RelativePosition

The bulk of the work here was in adding `dJ` as an output of `bodyKin`.

Resolves #466
That's a very good reason.  The question is whether people are using it yet.  

People are definitely using rigid body forces, but perhaps not writing their own forces yet.  Maybe it's better to change this now than later.  Unless anybody objects, I'd say go for it.

On Nov 2, 2014, at 7:12 AM, Andres Valenzuela <notifications@github.com> wrote:

> In systems/plants/@RigidBodyManipulator/bodyKin.m:
> 
> > @@ -1,4 +1,4 @@
> > -function [x,J,P] = bodyKin(obj,kinsol,body_or_frame_ind,pts)
> > +function [x,P,J,dP,dJ] = bodyKin(obj,kinsol,body_or_frame_ind,pts)
> I changed the order of the arguments to make it match our geval convention (x and P are the base outputs, so P should come before the first derivative of x). If that's not a good enough reason, I can definitely change it back. If it is, I can make sure that the calling functions are updated.
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