BUG: period partial string slicing failng again numpy master

[jreback]

xref: #7043

This fails on numpy master for some reason, can you investigate: https://travis-ci.org/pydata/pandas/jobs/25073475

[jreback]

cc @sinhrks

[sinhrks]

@jreback Thanks. Is it better to change DatetimeIndex.__getitem__ and PeriodIndex to raise ValueError to be comatible with np 1.8 or earlier? Or just leave as numpy does?

[jreback]

I am just skipping the tests, no biggie: 1b2ad6c

don't want to touch __getitem__ unless we have to, adds overhead

[sinhrks]

Understood. Thanks.