to_datetime() fails with Python 3.6
#### Code Sample

    pd.to_datetime('22/12/2016')

#### Problem description

This fails on Python 3.6.0, but works with previous versions like 3.5.2.  An exception is raised with 3.6:

    ValueError: Month out of range in datetime string "22/12/2016"

The error also occurs if `dayfirst=True` is passed to the function.

#### Expected Output
 
    2016-12-22 00:00:00

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS

commit: None
python: 3.6.0.final.0
python-bits: 64
OS: Linux
OS-release: 3.10.0
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.1
nose: None
pip: 9.0.1
setuptools: 27.2.0
Cython: None
numpy: 1.11.2
scipy: None
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2016.10
</details>
