Series.append() excepts with some funky overlapping dates
With pandas v0.8.0b1

In [90]: u
Out[90]: 
2012-05-08 01:45:00     86
2012-05-08 01:50:00    170
2012-05-08 01:55:00    130
2012-05-08 02:00:00    206
2012-05-08 02:05:00     52
2012-05-08 02:10:00      4
Freq: 5T

In [91]: u.append(u)

Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
  File "C:\Python27\lib\site-packages\pandas\core\series.py", line 1566, in append
    return concat(to_concat, ignore_index=False, verify_integrity=True)
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 836, in concat
    verify_integrity=verify_integrity)
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 895, in **init**
    self.new_axes = self._get_new_axes()
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1066, in _get_new_axes
    concat_axis = self._get_concat_axis()
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1097, in _get_concat_axis
    self._maybe_check_integrity(concat_axis)
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1106, in _maybe_check_integrity
    % str(overlap))
Exception: Indexes have overlapping values: [1970-01-16 225:45:00, 1970-01-16 225:50:00, 1970-01-16 225:55:00, 1970-01-16 226:00:00, 1970-01-16 226:05:00, 1970-01-16 226:10:00]
