printing a dataframe ignores timezone information of columns containing datetime64
I have a dataframe with a column containing dates (I do not want to use this column as the index of my dataframe). When printing the dataframe, the timezone information is lost. Directly accessing the _.values_ shows the correct timezone.

This might be related to #6415 

``` python
import pandas as pd

print "pandas version : ", pd.__version__

series = pd.to_datetime([1426374000000, 1426415697429], unit='ms').tz_localize('UTC').tz_convert('Europe/Berlin')
print '-- Printing series --'
print series
df = pd.DataFrame(series)
print '-- Printing df --'
print df
print '-- Printing df.values --'
print df.values
```

```
pandas version :  0.16.0
-- Printing series --
<class 'pandas.tseries.index.DatetimeIndex'>
[2015-03-15 00:00:00+01:00, 2015-03-15 11:34:57.429000+01:00]
Length: 2, Freq: None, Timezone: Europe/Berlin
-- Printing df --
                           0
0        2015-03-14 23:00:00
1 2015-03-15 10:34:57.429000
-- Printing df.values --
[['2015-03-15T00:00:00.000000000+0100']
 ['2015-03-15T11:34:57.429000000+0100']]
```
