to_clipboard doesn't support unicode
to_clipboard uses ascii encoding. And it cannot be changed.

```
>>> import pandas as pd
>>> pd.__version__
'0.17.0'
>>> pd.DataFrame(["Hello world"]).to_clipboard()
>>> pd.DataFrame(["Здравствуй, мир"]).to_clipboard()
...
UnicodeEncodeError: 'ascii' codec can't encode characters in position 22-31: ordinal not in range(128)
>>> pd.DataFrame(["Здравствуй, мир"]).to_clipboard(encoding="utf-8")
...
TypeError: to_string() got an unexpected keyword argument 'encoding'
```

Had to use part of to_clipboard source, where it exports dataframe to StringIO buffer, then put it to clipboard with Qt.
