Creating Series from DatetimeIndex w/ tz loses tz info
The original `DatetimeIndex` has the `tz`:

```
In [1]: pd.DatetimeIndex(
   ...:     pd.tseries.tools.to_datetime(['2013-1-1 13:00'], errors="raise")).tz_localize('US/Pacific')[0]
Out[1]: Timestamp('2013-01-01 13:00:00-0800', tz='US/Pacific')
```

But when converted to a `Series`, the `tz` info is lost:

```
In [2]: pd.Series(pd.DatetimeIndex(
   ...:     pd.tseries.tools.to_datetime(['2013-1-1 13:00'], errors="raise")).tz_localize('US/Pacific'))[0]
Out[2]: Timestamp('2013-01-01 21:00:00', tz=None)
```

If this is by design, then a warning would be nice. 

This issue came up when I tried to add a list of timezone aware dates to a DataFrame.
