Series/DataFrame repr fails for MultiIndex level names with unicode
``` python
In [34]: tuples = [t for t in product(range(2), range(2))]

In [35]: index = pandas.MultiIndex.from_tuples(tuples, names=[u'\u0394', 'i1'])

In [36]: df = pandas.DataFrame(np.random.randn(4,4), index=index)

In [37]: s = pandas.Series(range(4), index=index)

In[38]: df
...
UnicodeEncodeError: 'ascii' codec can't encode character u'\u0394' in position 0: ordinal not in range(128)

In[38]: s
...
UnicodeEncodeError: 'ascii' codec can't encode character u'\u0394' in position 0: ordinal not in range(128)

```
