failing microsecond formatter test
```
FAIL: pandas.tseries.tests.test_timeseries:TestTimeSeries.test_to_datetime_format_microsecond
  gvim -f +836 pandas/tseries/tests/test_timeseries.py  # test_to_datetime_format_microsecond
    self.assertEqual(result, exp)
AssertionError: Timestamp('2011-03-31 23:24:13.516352', tz=None) != datetime.datetime(2011, 4, 1, 0, 0, 1, 978000)

1 test, 1 failure, 0 errors in 0.0s
```

(i changed to `assertEqual`)
