Testr tests generate an AttributeError when run with latest subunit

Here is (most of) the traceback:

  File "/usr/lib/python2.7/threading.py", line 504, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib/python2.7/dist-packages/testtools/testsuite.py", line 100, in _run_test
    test.run(process_result)
  File "/usr/lib/python2.7/dist-packages/subunit/__init__.py", line 1160, in run
    protocol.lineReceived(line)
  File "/usr/lib/python2.7/dist-packages/subunit/__init__.py", line 549, in lineReceived
    self._state.lineReceived(line)
  File "/usr/lib/python2.7/dist-packages/subunit/__init__.py", line 386, in lineReceived
    self.details_parser.lineReceived(line)
  File "/usr/lib/python2.7/dist-packages/subunit/details.py", line 119, in lineReceived
    self._parse_state(line)
  File "/usr/lib/python2.7/dist-packages/subunit/details.py", line 84, in _look_for_content
    self._state.endDetails()
  File "/usr/lib/python2.7/dist-packages/subunit/__init__.py", line 381, in endDetails
    self._report_outcome()
  File "/usr/lib/python2.7/dist-packages/subunit/__init__.py", line 467, in _report_outcome
    details=self.details_parser.get_details("success"))
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 584, in addSuccess
    return self.decorated.addSuccess(test, details=details)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 698, in addSuccess
    return self.decorated.addSuccess(test, details=details)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 440, in addSuccess
    test, details=details)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 414, in _add_result_with_semaphore
    self.result.stopTest(test)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 643, in stopTest
    return self.decorated.stopTest(test)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 257, in stopTest
    return self._dispatch('stopTest', test)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 249, in _dispatch
    for result in self._results)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 249, in <genexpr>
    for result in self._results)
  File "/usr/lib/python2.7/dist-packages/testtools/testresult/real.py", line 643, in stopTest
    return self.decorated.stopTest(test)
  File "/home/benji/workspace/testr/latest/testrepository/results.py", line 36, in stopTest
    for method, args, kwargs in self._buffered_calls:
AttributeError: 'TestResultFilter' object has no attribute '_buffered_calls'