Incorrect result when using get_level_values on datetime index
Pandas 0.8.1:

```
import pandas as pd
import datetime as dt
tuples = [(dt.datetime(2012,1,1),1),(dt.datetime(2012,1,1),2),(dt.datetime(2012,1,2),1),(dt.datetime(2012,1,2),2)]
index = pd.MultiIndex.from_tuples(tuples)
index.get_level_values(level=0)
```

incorrectly returns:

```
array([1970-01-16 224:00:00, 1970-01-16 224:00:00, 1970-01-16 248:00:00,
       1970-01-16 248:00:00], dtype=datetime64[ns])
```
