need get_known_graph_ancestry() implementation

Imported from Debian bug http://bugs.debian.org/640164:

Package: bzr-hg
Version: 0.2.0~bzr511-1
Severity: normal

Attempting to view the tags in a Mercurial repository causes Bazaar to
crash:

=====
$ bzr info
/usr/lib/python2.6/dist-packages/lazr/restfulclient/__init__.py:19: UserWarning: Module paste was already imported from None, but /usr/lib/python2.6/dist-packages is being added to sys.path
  import pkg_resources
Standalone tree (format: hg)
Location:
  branch root: .

Related branches:
  parent branch: ssh://<email address hidden>/ned/coveragepy/

$ bzr log --log-format=line | wc -l
/usr/lib/python2.6/dist-packages/lazr/restfulclient/__init__.py:19: UserWarning: Module paste was already imported from None, but /usr/lib/python2.6/dist-packages is being added to sys.path
  import pkg_resources
984

$ bzr tags
/usr/lib/python2.6/dist-packages/lazr/restfulclient/__init__.py:19: UserWarning: Module paste was already imported from None, but /usr/lib/python2.6/dist-packages is being added to sys.path
  import pkg_resources
bzr: ERROR: exceptions.AttributeError: 'HgLocalRepository' object has no attribute 'revisions'

Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 923, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 1123, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 688, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 710, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/cleanup.py", line 135, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 1138, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/builtins.py", line 5517, in run
    revno = branch.revision_id_to_dotted_revno(revid)
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 140, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 377, in revision_id_to_dotted_revno
    return self._do_revision_id_to_dotted_revno(revision_id)
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 395, in _do_revision_id_to_dotted_revno
    result = self.get_revision_id_to_revno_map().get(revision_id)
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 140, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 412, in get_revision_id_to_revno_map
    mapping = self._gen_revno_map()
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 432, in _gen_revno_map
    in self.iter_merge_sorted_revisions())
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 140, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/branch.py", line 484, in iter_merge_sorted_revisions
    [last_revision])
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 140, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/repository.py", line 2706, in get_known_graph_ancestry
    known_graph = self.revisions.get_known_graph_ancestry(revision_keys)
AttributeError: 'HgLocalRepository' object has no attribute 'revisions'

bzr 2.3.1 on python 2.6.7 (Linux-3.0.0-1-powerpc64-ppc64-with-debian-wheezy-sid)
arguments: ['/usr/bin/bzr', 'tags']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_AU.UTF-8'
plugins:
  bash_completion /usr/lib/python2.6/dist-packages/bzrlib/plugins/bash_completion [2.3.1]
  builddeb /usr/lib/python2.6/dist-packages/bzrlib/plugins/builddeb [2.7.0dev]
  bzrtools /usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools [2.3.1]
  cvsps_import /usr/lib/python2.6/dist-packages/bzrlib/plugins/cvsps_import [unknown]
  etckeeper /usr/lib/python2.6/dist-packages/bzrlib/plugins/etckeeper [unknown]
  fastimport /usr/lib/python2.6/dist-packages/bzrlib/plugins/fastimport [0.11.0]
  git /usr/lib/python2.6/dist-packages/bzrlib/plugins/git [0.6.2]
  grep /usr/lib/python2.6/dist-packages/bzrlib/plugins/grep [0.4.0]
  hg /usr/lib/python2.6/dist-packages/bzrlib/plugins/hg [0.2.0dev]
  launchpad /usr/lib/python2.6/dist-packages/bzrlib/plugins/launchpad [2.3.1]
  loom /usr/lib/python2.6/dist-packages/bzrlib/plugins/loom [2.2.1dev]
  netrc_credential_store /usr/lib/python2.6/dist-packages/bzrlib/plugins/netrc_credential_store [2.3.1]
  news_merge /usr/lib/python2.6/dist-packages/bzrlib/plugins/news_merge [2.3.1]
  pipeline /usr/lib/python2.6/dist-packages/bzrlib/plugins/pipeline [1.1.0]
  pqm /usr/lib/python2.6/dist-packages/bzrlib/plugins/pqm [1.4.0dev]
  search /usr/lib/python2.6/dist-packages/bzrlib/plugins/search [1.7.0dev]
  stats /usr/lib/python2.6/dist-packages/bzrlib/plugins/stats [0.1.0]
  svn /usr/lib/python2.6/dist-packages/bzrlib/plugins/svn [1.0.5dev]
  upload /usr/lib/python2.6/dist-packages/bzrlib/plugins/upload [1.0.1dev]

*** 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.
=====

-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (990, 'testing'), (900, 'stable')
Architecture: powerpc (ppc64)

Kernel: Linux 3.0.0-1-powerpc64 (SMP w/2 CPU cores)
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_AU.utf8)
Shell: /bin/sh linked to /bin/dash

Versions of packages bzr-hg depends on:
ii bzr 2.3.1-2 easy to use distributed version co
ii mercurial 1.8.3-1 scalable distributed version contr
ii python 2.6.7-3 interactive high-level object-orie
ii python2.6 2.6.7-3 An interactive high-level object-o
ii python2.7 2.7.2-5 An interactive high-level object-o

bzr-hg recommends no packages.

bzr-hg suggests no packages.

-- no debconf information