Date slicing bug
This throws an exception

http://stackoverflow.com/questions/11306167/pandas-slicing-on-a-timeseries-seems-inconsistent-with-list-slicing

```
import pandas as pd
import datetime

times = [datetime.datetime(2000, 1, 1) + datetime.timedelta(minutes=i) for i in range(1000000)]
df = pd.TimeSeries(range(1000000), times)
df.ix[datetime.datetime(1900,1,1):datetime.datetime(2100,1,1)]
```
