GitWorkingTree.annotate_iter implementation

It would be very handy to be able use blame in git repos.

david_clymer@cruella-devel:~/Development/VistaShare/oct_git$ bzr blame README.txt
bzr: ERROR: exceptions.NotImplementedError: <bound method GitTexts.get_parent_map of <bzrlib.plugins.git.versionedfiles.GitTexts object at 0x3a05810>>

Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 924, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 1124, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 689, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 711, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/cleanup.py", line 135, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 1139, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/builtins.py", line 4682, in run
    show_ids=show_ids)
  File "/usr/lib/pymodules/python2.6/bzrlib/annotate.py", line 94, in annotate_file_tree
    annotations = list(tree.annotate_iter(file_id))
  File "/usr/lib/pymodules/python2.6/bzrlib/decorators.py", line 140, in read_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/workingtree.py", line 595, in annotate_iter
    for key, line in annotator.annotate_flat(this_key)]
  File "_annotator_pyx.pyx", line 275, in bzrlib._annotator_pyx.Annotator.annotate_flat (bzrlib/_annotator_pyx.c:2468)
  File "/usr/lib/pymodules/python2.6/bzrlib/_annotator_py.py", line 260, in annotate
    for text_key, text, num_lines in self._get_needed_texts(key, pb=pb):
  File "/usr/lib/pymodules/python2.6/bzrlib/_annotator_py.py", line 112, in _get_needed_texts
    keys, ann_keys = self._get_needed_keys(key)
  File "/usr/lib/pymodules/python2.6/bzrlib/_annotator_py.py", line 89, in _get_needed_keys
    next_parent_map.update(self._vf.get_parent_map(parent_lookup))
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/git/versionedfiles.py", line 123, in get_parent_map
    raise NotImplementedError(self.get_parent_map)
NotImplementedError: <bound method GitTexts.get_parent_map of <bzrlib.plugins.git.versionedfiles.GitTexts object at 0x3a05810>>

bzr 2.3.4 on python 2.6.6 (Linux-2.6.32-4-pve-x86_64-with-debian-6.0.2)
arguments: ['/usr/bin/bzr', 'blame', 'README.txt']
plugins: bash_completion[2.3.4], bzrtools[2.3.1], git[0.6.0],
    launchpad[2.3.4], netrc_credential_store[2.3.4], news_merge[2.3.4],
    svn[1.0.5dev]
encoding: 'ANSI_X3.4-1968', fsenc: 'ANSI_X3.4-1968', lang: 'C'

*** 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.