TST: Extend datetime64 arith tests to array classes, fix several broken cases
Some of the DateOffset arithmetic didn't work with the EA classes; this fixed that.  Other pieces of the DateOffset arithmetic will have to wait until TimedeltaArray gets a few more methods.
Hello @jbrockmendel! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/core/arrays/datetimelike.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/core/arrays/datetimelike.py) !

 - There are no PEP8 issues in the file [`pandas/core/arrays/datetimes.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/core/arrays/datetimes.py) !

 - There are no PEP8 issues in the file [`pandas/core/arrays/timedeltas.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/core/arrays/timedeltas.py) !

 - There are no PEP8 issues in the file [`pandas/core/ops.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/core/ops.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/conftest.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/tests/arithmetic/conftest.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_datetime64.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/tests/arithmetic/test_datetime64.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_period.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/tests/arithmetic/test_period.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_timedelta64.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/tests/arithmetic/test_timedelta64.py) !

 - There are no PEP8 issues in the file [`pandas/tseries/frequencies.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/tseries/frequencies.py) !

 - There are no PEP8 issues in the file [`pandas/tseries/offsets.py`](https://github.com/jbrockmendel/pandas/blob/1fbb5d53e938d5c7fb55d23fa30bfc38feccec53/pandas/tseries/offsets.py) !



##### Comment last updated on November 18, 2018 at 21:11 Hours UTC looks good. ping on green. > looks good. ping on green.

Travis fail is the test_apply segfault.  gentle ping thanks