BUG: GroupBy doesnt preserve timezone
Merge pull request #7099 from sinhrks/grouptz

BUG: GroupBy doesn't preserve timezone
BUG: remove unique requirement rom MultiIndex.get_locs to enable
     multi-index slicing on non-unique multi-indexes (GH7106)
Merge pull request #7107 from jreback/mi_slicers

BUG: remove unique requirement rom MultiIndex.get_locs (GH7106)
ENH/BUG: partial string indexing with PeriodIndex