fix: to_datetime returns KeyError: 'p' when %p specified in format string (GH5361)
closes https://github.com/pydata/pandas/issues/5361

pretty sure most of these tests are in

pandas/tseries/tests/test_timeseries.py

pls hook up Travis as well (see contributing.md)
 I realize that there is no real test coverage for to_datetime with various formats (there is SOME though). would you be up for moving this test (and the existing 2-3 tests) to a new class (within test_timeseries), then adding some coverage for formats? (a test like you did with the %p is enough).
 fixed and added tests, but tests with PM failed on one of Travis configurations (python 2.6), don't know what to do with that, so I commented tests
 do you want to try to debug the 2.6 error, you can use a virtual env
 @RomanPekar can you add a release notes entry for this? (under bug fixes for 0.13.1)
 @RomanPekar can you add release notes notes for this?
 @jreback Sorry had absolutely no time for last 2 months, spend all time with my family, I'll try to add notes ASAP
 @RomanPekar can you rebase?
 @jreback I'll try to find time tomorrow
 merged via https://github.com/pydata/pandas/commit/b5535b91278cb5712eb3b0f977e41b12c460d8d0
