[vtkusers] MetaImage support

[Rocky Rhodes]

I have used MetaIO headers for reading binary 3d image data files into itk.
I assumed the vtkImageReader would know about this format as well, but it
doesn't seem to.  I don't see anything in the documentation, but wondered if
there was a vtk MetaIO image reader anywhere; or support for any similar
format, where a small text header file contains a pointer to the file
containing the raw binary data.  Nrrd headers are like this as well.  I was
hopeful when I saw the vtk XML file formats, but didn't see any version of
these that allowed the binary data to reside in separate files.

Thanks for the help.

	Rocky