df.sort_values by 2 columns does not work in py3.5.1 but work in py2?
#### Code Sample, a copy-pastable example if possible

![image](https://cloud.githubusercontent.com/assets/5859702/17612924/3376d120-608a-11e6-8066-f4e0160c1518.png)

The code above works in py2 but not works in py3.
#### Expected Output

should get sorted dataframe.
#### output of `pd.show_versions()`

0.18.0
