BUG: PeriodIndex.unique results in Int64Index
Merge pull request #7843 from sinhrks/punique

BUG: PeriodIndex.unique results in Int64Index
TST: test for date parsing with removed infer_types arg
API: deprecate infer_types for real
TST: add wikipedia states table test
TST/DAT: add wikipedia data so we don't have to talk to the network