fix vtkPointGaussianRepresentation parallel rendering issues
vtkPointGaussianRepresentation was generating dataset without cells.
vtkRedistributeDataSet doesn't support redistributing data without
cells. Fixed vtkPointGaussianRepresentation for now by ensuring we
vtkPointGaussianRepresentation was also creating imbalanced MB which could cause vtkRedistributeDataSet deadlock. Fixed by letting the executive handle the looping over composite datasets -- simplifies the code, anyways.
vtkPointGaussianRepresentation was also not calling
vtkPVRenderView::SetOrderedCompositingConfiguration. Fixed that.