HACKING: add backslash to indicate line continuation and make it copy/pasteable
BUG FIX: use '/' as the path separator to match salt master.

On windows os.path.sep won't match the path separator used in lists of
paths returned by the master.

Minor optimization: calculate the probe string once ahead of the loop,
not each time around.
small optimization: Don't build string then immediately split to the same point.