AttributeError: 'Graph' object has no attribute 'iter_lefthand_ancestry' when uncommitting

[Stephan Hageboeck]

When uncommitting a very simple change, this happened:

bzr uncommit
  982 hageboeck 2015-07-06
      Fix typo in last commit.

The above revision(s) will be removed.
Are you sure [y/N]? y
bzr: ERROR: exceptions.AttributeError: 'Graph' object has no attribute 'iter_lefthand_ancestry'

Traceback (most recent call last):
  File "/usr/lib64/python2.6/site-packages/bzrlib/commands.py", line 853, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/bzrlib/commands.py", line 1055, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib64/python2.6/site-packages/bzrlib/commands.py", line 661, in run_argv_aliases
    return self.run_direct(**all_cmd_args)
  File "/usr/lib64/python2.6/site-packages/bzrlib/commands.py", line 665, in run_direct
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/bzrlib/cleanup.py", line 122, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/bzrlib/cleanup.py", line 156, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/bzrlib/builtins.py", line 4699, in run
    return self._run(b, tree, dry_run, verbose, revision, force, local=local)
  File "/usr/lib64/python2.6/site-packages/bzrlib/builtins.py", line 4751, in _run
    revno=revno, local=local)
  File "/usr/lib64/python2.6/site-packages/bzrlib/uncommit.py", line 111, in uncommit
    hook_new_tip)
  File "/lustre/user/hageboeck/.bazaar/plugins/gtk/__init__.py", line 131, in save_commit_messages
    commitmsgs.save_commit_messages(*args)
  File "/lustre/user/hageboeck/.bazaar/plugins/gtk/commitmsgs.py", line 101, in save_commit_messages
    revid_iterator = graph.iter_lefthand_ancestry(old_revid)
AttributeError: 'Graph' object has no attribute 'iter_lefthand_ancestry'

bzr 2.1.1 on python 2.6.6 (Linux-2.6.32-504.8.1.el6.x86_64-x86_64-with-redhat-6.6-Carbon)
arguments: ['/usr/bin/bzr', 'uncommit']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'
plugins:
  bzrtools /usr/lib64/python2.6/site-packages/bzrlib/plugins/bzrtools [2.1.0]
  gtk /lustre/user/hageboeck/.bazaar/plugins/gtk [0.104.0]
  launchpad /usr/lib64/python2.6/site-packages/bzrlib/plugins/launchpad [2.1.1]
  netrc_credential_store /usr/lib64/python2.6/site-packages/bzrlib/plugins/netrc_credential_store [2.1.1]
  news_merge /usr/lib64/python2.6/site-packages/bzrlib/plugins/news_merge [2.1.1]

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.

[Jelmer Vernooij (jelmer)]

Please upgrade to a newer version of bzr.