DateOffset & Timezones
```
tz = pytz.timezone('America/New_York')
tz.localize(datetime.datetime(2007,3,12)) - DateOffset(days=1)
# Timestamp('2007-03-11 00:00:00-0400', tz='America/New_York')
```

Shouldn't this be?

```
Timestamp('2007-03-11 00:00:00-0500', tz='America/New_York')
```
