BUG: Fix bug where DWIconvert does not load images.

This patch attempts to resolve http://www.na-mic.org/Bug/view.php?id=3023#c8249
bug.  the problem is that DWIConvert does not use the ITK IOFactory mechanism
to write images, and therefore the standard ITK shared library mechanisms do
not work for passing images back and forth to slicer.

This is resolved by forcing Slicer to use a command line version of
DWIConvert rather than the shared libary version.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21846 3bd1e089-480b-0410-8dfb-8563597acbee