Storing time zones HDFStore
Need to be careful to not break backwards compat (don't REQUIRE that time zone be stored in the hdf5 file)

```
In [10]: ts
Out[10]: 
2000-01-01 00:00:00-05:00    1.673428
2000-01-01 00:00:01-05:00   -0.647638
2000-01-01 00:00:02-05:00    0.185806
2000-01-01 00:00:03-05:00   -1.181972
2000-01-01 00:00:04-05:00    1.172915
2000-01-01 00:00:05-05:00   -1.058382
2000-01-01 00:00:06-05:00    0.716881
2000-01-01 00:00:07-05:00   -1.077554
2000-01-01 00:00:08-05:00   -1.347873
2000-01-01 00:00:09-05:00   -1.283497
2000-01-01 00:00:10-05:00   -0.628599
2000-01-01 00:00:11-05:00    1.681750
2000-01-01 00:00:12-05:00   -0.876274
2000-01-01 00:00:13-05:00   -0.137497
2000-01-01 00:00:14-05:00    1.199150
...
2000-01-02 03:46:25-05:00   -1.449709
2000-01-02 03:46:26-05:00    1.333123
2000-01-02 03:46:27-05:00   -0.306314
2000-01-02 03:46:28-05:00    0.040174
2000-01-02 03:46:29-05:00    0.823003
2000-01-02 03:46:30-05:00   -0.721399
2000-01-02 03:46:31-05:00   -2.812037
2000-01-02 03:46:32-05:00    0.721936
2000-01-02 03:46:33-05:00   -1.538009
2000-01-02 03:46:34-05:00    0.726892
2000-01-02 03:46:35-05:00    0.336684
2000-01-02 03:46:36-05:00    1.128328
2000-01-02 03:46:37-05:00    0.106069
2000-01-02 03:46:38-05:00   -1.167883
2000-01-02 03:46:39-05:00   -1.695608
Freq: S, Length: 100000

In [11]: store['bar']
Out[11]: 
2000-01-01 05:00:00    1.673428
2000-01-01 05:00:01   -0.647638
2000-01-01 05:00:02    0.185806
2000-01-01 05:00:03   -1.181972
2000-01-01 05:00:04    1.172915
2000-01-01 05:00:05   -1.058382
2000-01-01 05:00:06    0.716881
2000-01-01 05:00:07   -1.077554
2000-01-01 05:00:08   -1.347873
2000-01-01 05:00:09   -1.283497
2000-01-01 05:00:10   -0.628599
2000-01-01 05:00:11    1.681750
2000-01-01 05:00:12   -0.876274
2000-01-01 05:00:13   -0.137497
2000-01-01 05:00:14    1.199150
...
2000-01-02 08:46:25   -1.449709
2000-01-02 08:46:26    1.333123
2000-01-02 08:46:27   -0.306314
2000-01-02 08:46:28    0.040174
2000-01-02 08:46:29    0.823003
2000-01-02 08:46:30   -0.721399
2000-01-02 08:46:31   -2.812037
2000-01-02 08:46:32    0.721936
2000-01-02 08:46:33   -1.538009
2000-01-02 08:46:34    0.726892
2000-01-02 08:46:35    0.336684
2000-01-02 08:46:36    1.128328
2000-01-02 08:46:37    0.106069
2000-01-02 08:46:38   -1.167883
2000-01-02 08:46:39   -1.695608
Freq: S, Length: 100000

In [12]: store['bar'].index
Out[12]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[2000-01-01 05:00:00, ..., 2000-01-02 08:46:39]
Length: 100000, Freq: S, Timezone: None
```
