Bug#825923: python-nltk: nltk/tokenize/api.py imports ntlk.six which has been dropped

[Raphaël Hertzog]

Package: python-nltk
Version: 3.2.1-1
Severity: grave
Justification: renders package unusable
User: devel at kali.org
Usertags: origin-kali

I just got a report on Kali that w3af no longer works:
https://bugs.kali.org/view.php?id=3323

The stacktrace ends with this:
  File "/usr/lib/python2.7/dist-packages/nltk/tokenize/api.py", line 14, in
<module>
    from nltk.six import add_metaclass
ImportError: No module named six

The Debian patch use-six-package.diff is thus incomplete and should be updated
to also correct the import in nltk/tokenize/api.py.

Thank you for a quick fix (with urgency=high please so that it gets fixed in
testing quickly, thank you).

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (500, 'oldstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.5.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=fr_FR.utf8, LC_CTYPE=fr_FR.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)