pandas.tests.test_graphics error
When running nosetests on master i get one error.
This occurs when plotting  a dataframe with multiindex holding unicode.
It must be related to my environment since the [travis build](https://travis-ci.org/#!/pydata/pandas/jobs/2795124) passes.

python 2.7
numpy 1.6.2
matplotlib 1.1.0 (backend: Qt4Agg)

``` python
======================================================================
ERROR: test_plot (pandas.tests.test_graphics.TestDataFramePlots)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "<...>/pandas/tests/test_graphics.py", line 207, in test_plot
    _check_plot_works(df.plot, title=u'\u03A3')

<...>

<...>/lib/python2.7/site-packages/matplotlib/cbook.py", line 1832, in is_math_text
    "matplotlib display text must have all code points < 128 or use Unicode strings")
ValueError: matplotlib display text must have all code points < 128 or use Unicode strings
```
