Merge pull request #7598 from dstephens99/master

TST: Change nose.SkipTest to raise nose.SkipTest for io.data.Options.
ENH: look for index columns in row after header
BUG: DTI.freqstr raises AttributeError when freq is None
BUG: PeriodIndex.min/max returns int
Merge pull request #7606 from sinhrks/freqstr

BUG: DTI.freqstr raises AttributeError when freq is None
Merge pull request #7609 from sinhrks/pminmax

BUG: PeriodIndex.min/max returns int
API: DatetimeIndex and PeriodIndex have same representation
Merge pull request #7602 from sinhrks/periodrepr

API: DatetimeIndex and PeriodIndex have same representation
Removing Python2.6 CI dependencies to test import failures
Fix typo in documentation

Signed-off-by: Julien Danjou <julien@danjou.info>
Merge pull request #7613 from jd/master

Fix typo in documentation
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
Merge pull request #7610 from sinhrks/nanots

BUG: Timestamp.__new__ doesnt preserve nanosecond
BUG: Bug in to_timedelta that accepted invalid units and misinterpreted m/h (GH7611, GH6423)
Merge pull request #7616 from jreback/td

BUG: Bug in to_timedelta that accepted invalid units and misinterpreted m/h (GH7611, GH6423)
COMPAT: make numpy NaT comparison use a view to avoid implicit conversions
Merge pull request #7617 from jreback/nat2

COMPAT: make numpy NaT comparison use a view to avoid implicit conversions