ENH: Export DataFrame containing datetime with tz to HDF5 in fixed format
Hello,

I noticed a bug about exporting DataFrame with columns containing localized datetime. I might be due to some another required libraries updated...
Example : 

``` python
a = pd.to_datetime(['20120201', '20130201'])
b = pd.to_datetime(['20120201', '20130201'])
dfa = pd.DataFrame([a])
dfb = pd.DataFrame([b])
dfb[0] = dfb[0].dt.tz_localize('UTC')

dfa.to_hdf('tata.hdf', 'df') # success
dfb.to_hdf('toto.hdf', 'df') # fail
```

It works fine with Series
Thanks guys
