No bar when branch is locked with write lock.

[Martin Owens]

This traceback occurs in branches where there is a writelock from a process that failed to finish in bazaar and it's attempting to find the state of the branch.

Traceback (most recent call last):
  File "/home/doctormo/.nautilus/python-extensions/nautilus-groundcontrol.py", line 162, in get_widget
    return self.bazaar_choices(path, bar)
  File "/home/doctormo/.nautilus/python-extensions/nautilus-groundcontrol.py", line 309, in bazaar_choices
    changes = brch.get_changes()
  File "/home/doctormo/.nautilus/python-extensions/GroundControl/bazaar.py", line 108, in get_changes
    self.get_oldtree(), want_unversioned=True)
  File "/usr/lib/python2.6/dist-packages/bzrlib/tree.py", line 95, in changes_from
    want_unversioned=want_unversioned,
  File "<string>", line 13, in compare_read_locked
  File "/usr/lib/python2.6/dist-packages/bzrlib/inter.py", line 110, in unlock
    self.target.unlock()
  File "/usr/lib/python2.6/dist-packages/bzrlib/workingtree_4.py", line 1142, in unlock
    self._dirstate.save()
  File "/usr/lib/python2.6/dist-packages/bzrlib/dirstate.py", line 2293, in save
    grabbed_write_lock, new_lock = self._lock_token.temporary_write_lock()
  File "/usr/lib/python2.6/dist-packages/bzrlib/lock.py", line 270, in temporary_write_lock
    % (self.filename,))
AssertionError: file already locked: u'/home/doctormo/Projects/python/ground-control/translations/.bzr/checkout/dirstate'