BUG: Ensure Slicer dashboard packaging works if svn not in path

During recent windows factory maintenance, the path containing svn has
been removed from the PATH so that git bash could work with git svn.

As a side effect, dashboard windows packaging ceased to work.

Discussion: http://slicer-devel.65872.n3.nabble.com/Windows-nightly-not-on-download-page-tt4029503.html

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22241 3bd1e089-480b-0410-8dfb-8563597acbee