DataFrame.ix[tup, list] throws exception
per pydata email:

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I created a dataframe with multi index like this:
                      a   b   c
y        m d  
2000 1 1       1   2  3
             2       7   8  9
             3       4   5  6

...

it doesn't work to do this:  df.ix[(2000,1,1), ['a','b']]
## it gives KeyError = 1

in _NDFrameIndexer._getitem_tuple, the return value of the first ix._getitem_axis(key, axis=i) call returns a Series so the second call with axis=1 fails with KeyError=1
