Timestamp and DatetimeIndex construct different timezones
Question in the form of an issue: is this a bug?

```python
In [37]: pd.Timestamp('2000', tz='US/Central').tz == pd.DatetimeIndex(['2000'], tz='US/Central').tz
Out[37]: False
```

This leads to strange things like 

```python
In [38]: idx = pd.date_range('20170101', periods=4, tz='US/Pacific')

In [39]: idx[0].tz == idx.tz
Out[39]: False
```