KeyError raised out of DatetimeEngine formatted as int64
```
In [12]:

aapl[datetime(2011, 12, 7)]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/home/wesm/code/teaching/ga/<ipython-input-12-d32cb44b8294> in <module>()
----> 1 aapl[datetime(2011, 12, 7)]

/home/wesm/code/pandas/pandas/core/series.pyc in __getitem__(self, key)
    379     def __getitem__(self, key):
    380         try:
--> 381             return self.index.get_value(self, key)
    382         except InvalidIndexError:
    383             pass

/home/wesm/code/pandas/pandas/core/index.pyc in get_value(self, series, key)
   1747                 pass
   1748 
-> 1749             return self._engine.get_value(series, to_timestamp(key))
   1750 
   1751     def get_loc(self, key):

/home/wesm/code/pandas/pandas/_engines.so in pandas._engines.IndexEngine.get_value (pandas/src/engines.c:16263)()

/home/wesm/code/pandas/pandas/_engines.so in pandas._engines.IndexEngine.get_value (pandas/src/engines.c:16129)()

/home/wesm/code/pandas/pandas/_engines.so in pandas._engines.DatetimeEngine.get_loc (pandas/src/engines.c:20163)()

/home/wesm/code/pandas/pandas/_engines.so in pandas._engines.Int64HashTable.get_item (pandas/src/engines.c:5498)()

/home/wesm/code/pandas/pandas/_engines.so in pandas._engines.Int64HashTable.get_item (pandas/src/engines.c:5452)()

KeyError: 1323216000000000
```
