BUG/TST: fix tests for groupby nth on Series (GH7559)
BUG: GroupBy.size created by TimeGrouper raises AttributeError
Merge pull request #7580 from jreback/groupby_nth

BUG/TST: fix tests for groupby nth on Series (GH7559)
Merge pull request #7600 from sinhrks/bingrouper

BUG: GroupBy.size created by TimeGrouper raises AttributeError
BUG: Timestamp.__new__ doesnt preserve nanosecond