Code review comment for lp:~waigani/juju-core/1307241-isolate-from-jujud

I'm not sure what changed, but Tarmac really doesn't like this branch:
014-05-20 10:12:04 ERROR An error occurred trying to merge lp:juju-core: Server sent an unexpected error: ('error', 'GhostRevisionsHaveNoRevno', 'Could not determine revno for {<email address hidden>} because its ancestry shows a ghost at {tarmac-20140413170514-ii8w6q2fht3eiizi}')
2014-05-20 10:12:04 ERROR Traceback (most recent call last):
  File "/home/tarmac/tarmac/tarmac/bin/commands.py", line 385, in run
    merged = self._do_merges(branch)
  File "/home/tarmac/tarmac/tarmac/bin/commands.py", line 227, in _do_merges
    str(proposal.reviewed_revid))
  File "<string>", line 4, in revision_id_to_revno_read_locked
  File "/home/tarmac/.local/lib/python2.7/site-packages/bzrlib/remote.py", line 3885, in revision_id_to_revno
    self._remote_path(), revision_id)
  File "/home/tarmac/.local/lib/python2.7/site-packages/bzrlib/remote.py", line 75, in _call
    self._translate_error(err, **err_context)
  File "/home/tarmac/.local/lib/python2.7/site-packages/bzrlib/remote.py", line 3454, in _translate_error
    self.repository._translate_error(err, branch=self, **context)
  File "/home/tarmac/.local/lib/python2.7/site-packages/bzrlib/remote.py", line 1347, in _translate_error
    self.bzrdir._translate_error(err, repository=self, **context)
  File "/home/tarmac/.local/lib/python2.7/site-packages/bzrlib/remote.py", line 491, in _translate_error
    _translate_error(err, bzrdir=self, **context)
  File "/home/tarmac/.local/lib/python2.7/site-packages/bzrlib/remote.py", line 4194, in _translate_error
    raise errors.UnknownErrorFromSmartServer(err)
UnknownErrorFromSmartServer: Server sent an unexpected error: ('error', 'GhostRevisionsHaveNoRevno', 'Could not determine revno for {<email address hidden>} because its ancestry shows a ghost at {tarmac-20140413170514-ii8w6q2fht3eiizi}')