BUG: stack with datetimes

Just take from index itself, not levels.
TST: catch invalid options data parsing
Merge pull request #8053 from jreback/test_data

TST: catch invalid options data parsing
Merge pull request #8043 from TomAugspurger/stack-datetime

BUG: stack with datetimes
Don't call np.roll on empty arrays.

On some versions of numpy (such as 1.7, but not 1.8), this throws a
ZeroDivisionError.

Fixes #8019.