BUG: Don't return the same thing twice.

Surely this is a typo.

I noticed this because I was going add more robust parsing to datetools.parse [1], and I was surprised to find this function there. Two suggestions / questions. 1) Why not just roll this into the parse function like statsmodels instead of having it fall down on things like "1989Q1"? Extra function seems unneeded to me.

2) Why return the "resolution"? The parse function doesn't do this, and I'd expect them to have the same return signature. Optionally, the parse function should also try to infer a frequency.

[1] https://github.com/statsmodels/statsmodels/blob/master/statsmodels/tsa/base/datetools.py#L117