Slicing DateTimeIndex fails (KeyError)
I want to slice log files to extract only values within a certain time range. This works well with all but one log file. _"Must be the log file then!"_. However, the log file is well-formed like all the others and I don't see the reason my code fails:

``` python
import pandas as pan
import datetime as dt

time_f = '%Y-%m-%d %H:%M:%S.%f'

def get_sublog_by_index(log, t_stime, t_etime):
    s_idx, e_idx = log.index.slice_locs(t_stime, t_etime)
    return log.ix[s_idx: e_idx + 1]

if __name__ == '__main__':
    #http://pastebin.com/tQ6MFhgN
    df_good = pan.read_csv('dstat_good', header=True, parse_dates=True, index_col=0)
    #http://pastebin.com/M9r59Seq
    df_bad = pan.read_csv('dstat_bad', header=True, parse_dates=True, index_col=0)
    #manual construction just to be shure; why does pan.tslib.Timestamp.strptime fail?
    s_t_g = pan.tslib.Timestamp(dt.datetime.strptime('2015-04-23 03:46:37.030256', time_f))
    s_e_g = pan.tslib.Timestamp(dt.datetime.strptime('2015-04-23 04:46:40.560409', time_f))
    s_t_b = pan.tslib.Timestamp(dt.datetime.strptime('2015-04-23 02:44:49.310807', time_f))
    s_e_b = pan.tslib.Timestamp(dt.datetime.strptime('2015-04-23 03:44:52.922636', time_f))
    sublog_g = get_sublog_by_index(df_good, s_t_g, s_e_g)
    sublog_b = get_sublog_by_index(df_bad, s_t_b, s_e_b)
```

I have two log files to test, one working, the other not:
http://pastebin.com/tQ6MFhgN (working)
http://pastebin.com/M9r59Seq (not working)

At closer inspection you will notice that the start and end times (`s_t*` and `s_e*`) are within the range of the logs' timestamps. You will also notice that the _bad_ log has no odd data or anything else that gives a hint why the code is not working in that case. This is truly odd and seems to origin from the deep. Or I'm struck with utter blindness?

For completeness, this is what I get if I try to slice the _bad_ log file:

```
  ...
  File "/usr/local/bin/dstatlogsplit", line 54, in get_sublog_by_index
    s_idx, e_idx = log.index.slice_locs(t_stime, t_etime)
  File "/usr/local/lib/python2.7/dist-packages/pandas/core/index.py", line 2484, in slice_locs
    start_slice = self.get_slice_bound(start, 'left', kind)
  File "/usr/local/lib/python2.7/dist-packages/pandas/core/index.py", line 2432, in get_slice_bound
    raise err
KeyError: 1429757089310807000L
```
