xaxis.min / xaxis.max breaks the graph when passed a raw date object

[danieljpetersen]

It appears that the options xaxis.min and xaxis.max do not work when given a date object.

I've made a fiddle of the problem -- https://jsfiddle.net/jgz0fb28/1/

I eventually figured out that you need to give it date.getTime() for it to work as expected, but this was really non-obvious to me. I feel like it should explicitly handle this case, or at least document it somewhere (did I just miss it?).