BUG: Scipy interpolate methods are not datetime64 aware
From [this SO question](http://stackoverflow.com/questions/21169182/interpolation-for-some-methods-is-failing-with-a-type-error).

Is this something we should worry about here, or report upstream to scipy? The workaround I posted on SO is just to explicitly recast the index as an int64, interpolate on that, and then reset the original index. Any reason we shouldn't do this internally?
