Fix bad caching in DynamicPointVisualizer.

We were not only performing a bad color comparison, we were also caching a reference instead of cloning.  This resulted in point textures never being udpated to reflect the underlying DynamicPoint changes.

@shunter this is the issue I was just discussing with you.
Merge pull request #552 from AnalyticalGraphicsInc/fixPoints

Fix bad caching in DynamicPointVisualizer.