Try to fix buildbot error in other way.

The internal unicode database is now always used.

(after 5 years: see
  http://mail.python.org/pipermail/python-dev/2004-December/050193.html
)

  to Doc/license.rst.

with Python2.7.

ZipFile.open()) could return more bytes than requested.

Instead of the locale encoding.

mbcs (Windows default filesystem encoding) is now strict by default, and
depending on the code page, TESTFN_UNICODE may not be encodable to bytes.

Remove also unused "encoded" argument from _do_directory() method.

a non-ASCII byte in the format string.

Document also the encoding.

os.listdir(str) always returns unicode and it can return non-ascii filenames
even if supports_unicode_filenames is False.