Adapted Brian Curtin's http://bugs.python.org/file15381/
shutil_which.patch and made another reference implementation as a standalone module including the following fixes:

* uses ``PATHEXT`` on Windows
* searches current directory before ``PATH`` on Windows, but not before an explicitly passed path
* accepts both string or iterable for an explicitly passed path, or pathext
* accepts an explicitly passed empty path, or pathext (either '' or [])
* does not search ``PATH`` for files that have a path specified in their name already

Use any of these changes in the final shutil patch if you like to. The shutil module has availability 'Unix, Windows' after all.