create another VertexData array in RToVTKTree

The "true node weight" array is also created when we read in a tree
using the vtkNewickTreeReader.  This array is currently the best
basis of comparison that we have for the vtkTreeDifferenceFilter.

Change-Id: Iae7f8830f0c611d1aaca957e8a0651426d171da8
better support for vtkCompositeDataSet output

Allow the vtkCompositeDataSet to contain of any type of vtkDataObject.
Previously, this class assumed that all of the components of the
vtkCompositeDataSet were vtkDataSets.

In order to properly handle vtkCompositeDataSet output, I also had to
add new code within RequestData() to initialize the components of the
output.  Without this change, the output would merely contain the
components of the input vtkCompositeDataSet.

Change-Id: If9c3a83910af99095362919a50d29c6bb3b6db0f
fix error message

Before this change, the wrong name was mentioned when the comparison
array does not exist.

Change-Id: Ib4cee14ae78c5d111ecd245c2d4ab7f553aed8e2
minor cleanup

remove debug message, plug memory leak

Change-Id: If9fc08f0e046bcf89c0d14efc377b12d1a278605
better support for comparing identical trees

we now treat this as a special case to make sure that the difference
tree is visualized all in grey.

Change-Id: I3718a8e1989ffd7060a5bcce599e010941572dda
Merge topic 'improve_RCalc_composite' into master

3a7a8a26 better support for comparing identical trees
63533d6d minor cleanup
1682dea4 fix error message
6f11bfee better support for vtkCompositeDataSet output
833aadb5 create another VertexData array in RToVTKTree