BUG: #3561 handle paths for windows

Earlier versions of the tpycl (tcl/python) layer worked on all
platforms, but apparently a change occured (maybe the
cmakeified python?) that led to a different interpretation
of this path and now native windows paths with backslashes
are returned from os.path.  As a result we need to convert the
paths before sending them to tcl, which always uses forward
slashes for standard directory operations on all platforms.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23066 3bd1e089-480b-0410-8dfb-8563597acbee