API: DateTimeIndex slicing removes name label
Shouldn't it carry all possible properties instead?

Steps to reproduce:

``` python

import pandas as pd


st = pd.Timestamp('2013-07-01 00:00:00', tz='America/Los_Angeles')
et = pd.Timestamp('2013-07-02 00:00:00', tz='America/Los_Angeles')

dr = pd.date_range(st, et, freq='H', name='timebucket')
assert dr.name == 'timebucket'
dr = dr[1:]
assert dr.name == None
```
