tutorial assumes format_timezone() returns only offset int, not tuple

When the parse_timezone() function from dulwich.objects is used to generate a value for commit.commit_timezone and commit.author_timezone a Type Error is raised by format_timezone().

Traceback (most recent call last):
  File "/usr/lib/python2.6/pprint.py", line 59, in pformat
    return PrettyPrinter(indent=indent, width=width, depth=depth).pformat(object)
  File "/usr/lib/python2.6/pprint.py", line 111, in pformat
    self._format(object, sio, 0, 0, {}, 0)
  File "/usr/lib/python2.6/pprint.py", line 129, in _format
    rep = self._repr(object, context, level - 1)
  File "/usr/lib/python2.6/pprint.py", line 223, in _repr
    self._depth, level)
  File "/usr/lib/python2.6/pprint.py", line 235, in format
    return _safe_repr(object, context, maxlevels, level)
  File "/usr/lib/python2.6/pprint.py", line 320, in _safe_repr
    rep = repr(object)
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 460, in __repr__
    return "<%s %s>" % (self.__class__.__name__, self.id)
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 448, in id
    return self.sha().hexdigest()
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 440, in sha
    new_sha.update(self._header())
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 419, in _header
    return object_header(self.type, self.raw_length())
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 424, in raw_length
    for chunk in self.as_raw_chunks():
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 220, in as_raw_chunks
    self._chunked_text = self._serialize()
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 983, in _serialize
    self._author_timezone_neg_utc)))
  File "/home/ryan/.virtualenvs/jam-try/lib/python2.6/site-packages/dulwich-0.6.1-py2.6.egg/dulwich/objects.py", line 878, in format_timezone
    if offset % 60 != 0:
TypeError: unsupported operand type(s) for %: 'tuple' and 'int'

This issue can be worked around by using:

commit.commit_timezone = commit.author_timezone = parse_timezone('-0600')[0]

which returns the integer expected by format_timezone()