[vtkusers] filter for non-vtkDataObject input/ouput

[dean.inglis at camris.ca]

HI, I am trying to develop a filter to take as input a vtkColorTransferFunction,
modify it, and then output a vtkColorTransferFunction, similar to what
is done with vtkPiecewiseFunctionShiftScale.  The problem is that
vtkColorTransferFunction is not a vtkDataObject, which seems to be
required of all classes inherited from vtkAlgorithm.  Is there a vtkAlgorithm
subclass that I could model the required pipeline behavior from?

thanks,
Dean