Fix for #247

If you do a pjax request, then reload the page, and then hit back, the state is pushed (the url updates) but because the reload cleared the cache the container does not change.

This fix currently breaks 'no initial pjax:popstate event'

I'm having a hard time figuring out exactly why that test is doing what its doing.

It seems to me when you load a page, do a pjax request, go back and then go forward, you don't want the pjax:popstate event firing on the go forward. But I can't work out why?