[vtkusers] Graph scaling question

[Tim Newsham]

> works pretty well.  However, I would prefer that the interaction
> of the model appear the same before and after scaling..  By
> this I mean, the graph shouldnt appear to move, and the interactor
> should still rotate around the same point.  

Answering my own question, in case anyone else cares about the answer.
Scaling has to be done with respect to the camera's focal point.  After
that, everything was honkey dorey.