Pandas DataFrame.to_json() does a Segmentation fault with data datetime64[ns, TimeZone]
This is the working example 

```
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ uname -a
Linux app01 3.13.0-48-generic #80-Ubuntu SMP Thu Mar 12 11:16:15 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ python --version
Python 2.7.6
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ pip list | grep num
You are using pip version 7.0.3, however version 7.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
numpy (1.10.1)
phonenumbers (6.0.0a0)
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ pip list | grep pandas
You are using pip version 7.0.3, however version 7.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
pandas (0.17.1)
env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ python 
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> df = pd.DataFrame({'A' : pd.date_range('20130101',periods=3), 'B' : pd.date_range('20130101',periods=3,tz='US/Eastern'), 'C' : pd.date_range('20130101',periods=3,tz='CET')})
>>> df.dtypes
A                datetime64[ns]
B    datetime64[ns, US/Eastern]
C           datetime64[ns, CET]
dtype: object
>>> df.to_json()
Segmentation fault (core dumped)
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ 
```

The only solution I found is to remove tz_localize(None)

```
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ python 
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> df = pd.DataFrame({'A' : pd.date_range('20130101',periods=3), 'B' : pd.date_range('20130101',periods=3), 'C' : pd.date_range('20130101',periods=3)})
>>> df.to_json()
'{"A":{"0":1356998400000,"1":1357084800000,"2":1357171200000},"B":{"0":1356998400000,"1":1357084800000,"2":1357171200000},"C":{"0":1356998400000,"1":1357084800000,"2":1357171200000}}'
>>> 
(env)vagrant@app01:~/repos/peppertap_v1/shopper_bot$ 
```
