TST: Change nose.SkipTest to raise nose.SkipTest for io.data.Options.
Merge pull request #7598 from dstephens99/master

TST: Change nose.SkipTest to raise nose.SkipTest for io.data.Options.
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