TST: PeriodIndex pickle roundtrip does not recreate freq GH2891
BUG: PeriodIndex pickle roundtrip does not recreate freq GH2891
Merge pull request #3224 from y-p/GH2891

PeriodIndex pickle roundtrip does not recreate freq GH2891
DOC: update RELEASE.rst
BLD: Compact builds to fit into travis's 5-job concurrency limit
DOC: update CONTRIBUTING.md
BLD: travis revamped their log, be verbose with abandon