Calling xs on DataFrame with index but no columns raises Exception
example:

```
In [1]: df = DataFrame(index=['a', 'b', 'c'])

In [2]: df.ix['a']
ERROR: An unexpected error occurred while tokenizing input
The following traceback may be corrupted or invalid
The error message is: ('EOF in multi-line statement', (2, 0))

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/home/wesm/code/pandas/<ipython-input-2-6181dcf1ffea> in <module>()
----> 1 df.ix['a']

/home/wesm/code/pandas/pandas/core/indexing.pyc in __getitem__(self, key)
    102             return self._fancy_getitem(key, axis=0)
    103         else:
--> 104             return self._fancy_getitem_axis(key, axis=0)
    105 
    106     def __setitem__(self, key, value):

/home/wesm/code/pandas/pandas/core/indexing.pyc in _fancy_getitem_axis(self, key, axis)
    200                 return self.frame.xs(idx)
    201             else:
--> 202                 return self.frame.xs(idx, copy=False)
    203         else:
    204             col = key

/home/wesm/code/pandas/pandas/core/frame.pyc in xs(self, key, copy)
    839 
    840         self._consolidate_inplace()
--> 841         values = self._data.xs(key, axis=1, copy=copy)
    842         return Series(values.as_matrix(), index=self.columns)
    843 

/home/wesm/code/pandas/pandas/core/internals.pyc in xs(self, key, axis, copy)
    451                 new_blocks.append(newb)
    452         else:
--> 453             vals = self.blocks[0].values[slicer]
    454             if copy:
    455                 vals = vals.copy()

IndexError: list index out of range
```
