COMP: Ensure itkFactoryRegistration code is included when building against ITKv4

See http://www.na-mic.org/Bug/view.php?id=2900

Fixes #2900

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21652 3bd1e089-480b-0410-8dfb-8563597acbee