os.listdir(str) always returns unicode and it can return non-ascii filenames
even if supports_unicode_filenames is False.
........
r84784 | victor.stinner | 2010-09-13 21:41:36 +0200 (lun., 13 sept. 2010) | 2 lines
Issue #767645: Set os.path.supports_unicode_filenames to True on Mac OS X
(macpath module).
........