Comparisons between datetime64[ns]
#### Code Sample, a copy-pastable example if possible
**content of dataframe j**
_REFERENCIA FECHAPROGRAMA FECHAENVIO  NECESIDAD_
0       81007104    2015-04-04 2016-01-04     1038.0
1       81007104    2015-04-11 2016-01-04     1281.0
4       81007104    2015-04-18 2016-01-04     1172.0
...
1228    81007104    2015-12-05 2016-01-28      180.0
...
1541    81007104    2016-01-02 2016-01-29      180.0
1639    81007104    2016-01-09 2016-01-29      360.0
1734    81007104    2016-01-16 2016-01-29      360.0
1833    81007104    2016-01-23 2016-01-29      360.0

and the code is 
```python
a = j['FECHAENVIO'][-1:]
print(j['FECHAENVIO'][0] == a) #False 
print(j[j['FECHAENVIO'] == a]) #ValueError: Can only compare identically-labeled Series objects

```
#### Problem description

I have part of a dataframe groupby REFERENCIA, and now I wanted to get all rows with the last day in FECHAENVIO, for that I tried to get the last date in FECHAENVIO, save it in a, and then compare all the column with this date.

After checking SO and not able to find anything related to it, I found the issue #17965 and I think is relate to it, but not sure.

After 2 hours I did a workaround using FECHAENVIO as the index and using j.last('1D'), but I thought it was better to inform of the possible bug.


#### Expected Output

A dataframe with rows in which FECHAENVIO is equals to the variable a.

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

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.0.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 142 Stepping 9, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.23.4
pytest: 3.8.0
pip: 18.1
setuptools: 40.2.0
Cython: 0.28.5
numpy: 1.15.4
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 6.5.0
sphinx: 1.7.9
patsy: 0.5.0
dateutil: 2.7.5
pytz: 2018.5
blosc: None
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.8
feather: None
matplotlib: 2.2.3
openpyxl: 2.5.6
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.1.0
lxml: 4.2.5
bs4: 4.6.3
html5lib: 1.0.1
sqlalchemy: 1.2.11
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
</details>
