ThreadsafeForwardingResult does not forward time outside of tests

ThreadsafeForwardingResult does not forward time outside of tests, as this test demonstrates:

    def test_time_going_through_threadsafe_filter(self):
        # ThreadsafeForwardingResult discards time() output that is not bound
        # specifically to the start or end of a test.
        result = TestResult()
        filtered = ThreadsafeForwardingResult(result, Semaphore(1))
        filtered.startTestRun()
        filtered.time(datetime(2011, 1, 1, 0, 0, 1))
        filtered.startTest(self)
        filtered.time(datetime(2011, 1, 1, 0, 0, 2))
        filtered.addSuccess(self)
        # This will be ignored.
        filtered.time(datetime(2011, 1, 1, 0, 0, 3))
        filtered.stopTest(self)
        filtered.stopTestRun()
        self.assertEqual(datetime(2011, 1, 1, 0, 0, 3), result._now())

This makes the resulting stream of events slightly less valuable for time analysis. In particular, it would be useful to have the very first time event and the very last time event for a particular stream.