ERR: tz_localize ambiguous ='infer'  
Hello, 

a problem concerning  DST with change time. My df has a index  for the year 2013 each 15 minutes. 

```python
df.index.tz_localize('Europe/Zurich',ambiguous = 'infer')
```
output:
 AmbiguousTimeError: 2013-10-27 02:00:00

The input DateTimeindex is:
...
              '2013-10-27 01:30:00', '2013-10-27 01:45:00',
              '2013-10-27 02:00:00', '2013-10-27 02:15:00',
               '2013-10-27 02:30:00', '2013-10-27 02:45:00',
               '2013-10-27 03:00:00', '2013-10-27 02:15:00',
               '2013-10-27 02:30:00', '2013-10-27 02:45:00',
               '2013-10-27 03:00:00', '2013-10-27 03:15:00',
               '2013-10-27 03:30:00', '2013-10-27 03:45:00',
...
 
I would like an output DateTimeindex like:
output:
...
               '2013-10-27 01:30:00+02:00', '2013-10-27 01:45:00+02:00',
               '2013-10-27 02:00:00+02:00', '2013-10-27 02:15:00+02:00',
               '2013-10-27 02:30:00+02:00', '2013-10-27 02:45:00+02:00',                   
               '2013-10-27 03:00:00+02:00', '2013-10-27 02:15:00+01:00',
               '2013-10-27 02:30:00+01:00', '2013-10-27 02:45:00+01:00', 
               '2013-10-27 03:00:00+01:00', '2013-10-27 03:15:00+01:00',
               '2013-10-27 03:30:00+01:00', '2013-10-27 03:45:00+01:00',
...


Thank you

```python
pd.show_versions()
```
<details>
output:
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Darwin
OS-release: 15.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: fr_CH.UTF-8
LOCALE: fr_CH.UTF-8

pandas: 0.19.1
nose: 1.3.7
pip: 8.1.2
setuptools: 21.2.1
Cython: None
numpy: 1.11.2
scipy: 0.17.1
statsmodels: None
xarray: None
IPython: 4.2.0
sphinx: None
patsy: None
dateutil: 2.5.3
pytz: 2016.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: 1.0.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None
</details>
