TST: fix up bench/bench_merge.py
BUG: raise exception when view not possible of multiindex'd dataframe. close #2117
BUG: start_time end_time to_timestamp bugs #2124 #2125 #1764
BUG: change default frequency for to_timestamp
BUG: add same to_timestamp change to PeriodIndex
BUG: groupby.first/last datetime64 type issue. close #2133
BUG: off-center grid in case of stacked bar plot #2157
TST: get rid of string.letters import for py3
BUG: align two tz aware frames loses tz #2127
Merge remote branch 'chang/to-timestamp'

* chang/to-timestamp:
  BUG: add same to_timestamp change to PeriodIndex
  BUG: change default frequency for to_timestamp
  BUG: start_time end_time to_timestamp bugs #2124 #2125 #1764
ENH: nanosecond tweak per #2170. period spanning in upsampling
BUG: better floating point robustness in moving window functions. close #2114
BUG: fix NA handling in ewma adjustment. close #2128
BUG: Series.diff for integer dtypes #2087
BUG: int dtype diff for frame. refactored diff into common
ENH: generify common.diff per #2174, close #2087
ENH: specialized cython diff functions
BUG: MultiIndex.__getitem__ failure with NA values causing downstream problems. close #2008
BUG: basic DataFrame constructor refactoring to better support duplicate columns. close #2079
BUG: stop overridding matplotlib unit registrations for datetime.datetime/date/time but keep registration for pandas specific classes Period and Timestamp