BUG: fix paths for DICOM executable searches

Since the helper executables are not in the slicer bin directory
for a local build of slicer, be sure to also check in the DCMTK-build
bin directory to find the actual executable.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21870 3bd1e089-480b-0410-8dfb-8563597acbee