Index is not hashable
``` python
hash(df.index)
> /home/user1/src/pandas/pandas/core/index.py(346)__hash__()
    345     def __hash__(self):
--> 346         return hash(self.view(np.ndarray))
    347 

/home/user1/src/pandas/pandas/core/index.pyc in __hash__(self)
    344 
    345     def __hash__(self):
--> 346         return hash(self.view(np.ndarray))
    347 
    348     def __setitem__(self, key, value):

TypeError: unhashable type: 'numpy.ndarray'
```
