BUG: timezone offset double counted using date_range
BUG: DateTimeIndex.append broken with tz-aware indices
BUG: Unstack of a frame with no nans would always cause dtype upcasting (GH2929_)
Merge pull request #2935 from stephenwlin/daterange_tz

BUG: timezone offset double counted using date_range and DateTimeIndex.append (fixes #2906, #2938)
BUG: Bug in DataFrame combine_first where non-specified values could cause dtype changes (GH3041_)
Merge pull request #3040 from jreback/unstack

BUG: Unstack of a frame with no nans would always cause dtype upcasting (GH #2929)
Merge pull request #3043 from jreback/combine_3016

BUG: frame combine_first where non-specified values could cause dtype changes (#3041)
BUG: Bug in groupby with first/last where dtypes could change (GH3041_)
DOC: docstring updates in core/common.py for _possibily_cast_to_timedelta
Merge pull request #3044 from jreback/groupby_3016

BUG: Bug in groupby with first/last where dtypes could change (GH3041_)
TST: str.contains respects na parameter, GH2806
BUG: str.contains ignored na argument GH2806