DatetimeIndex formatting spills outside 80 characters
```
In [25]: with pd.option_context('display.width', 80):
    ...:     print(pd.date_range('20170101 12:00:00', periods=2))
    ...:     
    ...:     
DatetimeIndex(['2017-01-01 12:00:00', '2017-01-02 12:00:00'], dtype='datetime64[ns]', freq='D')

In [26]: with pd.option_context('display.width', 80):
    ...:     print(pd.date_range('20170101 12:00:00', periods=4))
    ...:     
    ...:     
    ...:     
DatetimeIndex(['2017-01-01 12:00:00', '2017-01-02 12:00:00',
               '2017-01-03 12:00:00', '2017-01-04 12:00:00'],
              dtype='datetime64[ns]', freq='D')
```