Add an adapter to make enhanced MR look like non-enhanced MR.

The purpose of this is to allow the generator to use an enhanced
data set as its "source", even though the generated data will be
a non-enhanced data set.
Adapter also needed for one attribute in vtkDICOMMRGenerator.
Adapter should report NumberOfFrames as not set.
Add a utility called "dicomtodicom".

Currently, this utility doesn't do much.  It reads a DICOM series, and
then writes it back out, optionally as an MPR of the original series.
One if its main purposes is to allow testing of the vtkDICOMGenerator.