failure in multiindex-based access in  Panel
Example:

import pandas as pn
ind = pn.MultiIndex.from_tuples([('a', 1), ('a', 2), ('b', 1), ('b',2)], names=['fist', 'second'])
wp = pn.Panel(np.random.random((4,5,5)), items=ind,
major_axis=np.arange(5), minor_axis=np.arange(5))

In [10]: wp['a']
...
KeyError: 'no item named a'

In [11]: wp.ix['a']
...
KeyError: 'no item named a'
