fix path.py wrapper for non-string arguments

this code:

    path("MANIFEST.in").write_lines("include %s" % x for x in MANIFEST)

works perfectly fine with regular path.py, but the paver.path wrapper function assumes that every argument is going to be a string when it calls ``''.join(args)``

this change forces wrapping them in ``repr()``so that uses like the one above won't needlessly break.