I think we should be careful enough to tackle on this.
iszegedi's patch seems to work correctly,
but XBD's spec itself has some defect.
http://www.opengroup.org/austin/mailarchives/ag-review/msg01722.html

What do you think of the follow behavior?
>>> os.mkdir('dir/')
>>> os.mkdir('dir2/')
>>> os.rmdir(os.path.normpath('dir'))
>>> os.rmdir(os.path.normpath('dir2/'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 22] Invalid argument: 'dir2/.'