Remove an obsolete comment from vtkDICOMWriter.
Add a caveat to the MatchInstances method in the generator.
Add computation of Largest/Smalles pixel per image.
Add the VOI LUT module to round things out.

It is important for image viewing software to have a viewing window
in the DICOM file, because otherwise the image will show up as too
dark.  No support for look-up tables yet.