.loc[] assignment gives broadcast error
``` python
In [8]: wp = Panel(randn(2, 5, 4), items=['Item1', 'Item2'], major_axis=date_range('1/1/2000', periods=5), minor_axis=['A', 'B', 'C', 'D'])

In [9]: wp2 = Panel(randn(2, 5, 4), items=['Item1', 'Item2'], major_axis=date_range('1/1/2000', periods=5), minor_axis=['A', 'B', 'C', 'D'])

In [10]: wp.loc[['Item1', 'Item2'], :, ['A', 'B']]
Out[10]: 
<class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 5 (major_axis) x 2 (minor_axis)
Items axis: Item1 to Item2
Major_axis axis: 2000-01-01 00:00:00 to 2000-01-05 00:00:00
Minor_axis axis: A to B

In [11]: wp.loc[['Item1', 'Item2'], :, ['A', 'B']] = wp2.loc[['Item1', 'Item2'], :, ['A', 'B']]
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-11-275f8d9be664> in <module>()
----> 1 wp.loc[['Item1', 'Item2'], :, ['A', 'B']] = wp2.loc[['Item1', 'Item2'], :, ['A', 'B']]

/usr/local/lib/python2.7/dist-packages/pandas/core/indexing.pyc in __setitem__(self, key, value)
     85             indexer = self._convert_to_indexer(key)
     86 
---> 87         self._setitem_with_indexer(indexer, value)
     88 
     89     def _has_valid_tuple(self, key):

/usr/local/lib/python2.7/dist-packages/pandas/core/indexing.pyc in _setitem_with_indexer(self, indexer, value)
    182             values = self.obj.values
    183             if np.prod(values.shape):
--> 184                 values[indexer] = value
    185 
    186     def _align_series(self, indexer, ser):

ValueError: array is not broadcastable to correct shape
```

Those should be the same shape so I don't see why this assignment shouldn't work. This is with pandas 0.11.0.
