BUG: PeriodIndex.unique results in Int64Index
COMPAT: SettingWithCopy will now warn when slices which can generate views
        are then set
Merge pull request #7845 from jreback/setting_with_copy

COMPAT: SettingWithCopy will now warn when slices which can generate views are then set
Merge pull request #7843 from sinhrks/punique

BUG: PeriodIndex.unique results in Int64Index