deriving from it.  vtkKdTreePointLocator is just a wrapper class for vtkKdTree so that it can be
used as a point locator instead of vtkPointLocator since the kd tree locator is much faster for
most situations.

vtkKdTree and its dependencies were moved from Graphics to Filtering so that Filtering wouldn't
be dependent on Graphics.

I also added in some tests for the point locators.

PERF: Changes in vtkKdTree and vtkPointSet to make searches faster.