where() corrupts tz-aware datetime column data
#### Code Sample, a copy-pastable example if possible

```python
# Your code here

s = pd.Series([pd.Timestamp(s) for s in ['2016-12-31 12:00:04+00:00', '2016-12-31 12:00:04.010000+00:00']])
p = pd.Series([False, True])
s.where(p)

```
#### Problem description

receive

0                                   NaT
1   2016-12-31 12:00:04.009999872+00:00

seems similar to https://github.com/pandas-dev/pandas/issues/14872, which I also ran into.

works as expected if you do: s.where(p, other=pd.NaT)

#### Expected Output

I would expect:

0                                NaT
1   2016-12-31 12:00:04.010000+00:00

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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.1.35
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.2
nose: None
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.24.1
numpy: 1.11.2
scipy: 0.18.1
statsmodels: 0.6.1
xarray: None
IPython: 5.1.0
sphinx: 1.4.6
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.6.1
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.5.2
matplotlib: 1.5.1
openpyxl: 2.3.2
xlrd: 1.0.0
xlwt: None
xlsxwriter: 0.9.3
lxml: None
bs4: 4.5.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.13
pymysql: None
psycopg2: None
jinja2: 2.9.4
boto: None
pandas_datareader: None

</details>
