Fixes #306

It seems that the `popped` variable was only there to detect state changes. The problem was that after page was reloaded the `popped` was automatically set to `false` (of course) which caused the `onpopstate` event to be practically ignored. One possible solution is to make the variable survive page reload or at least hot code push. Another option, which I considered the right one, is not to use `popped` variable at all, and only compare the current and previous states when the state is actually changed. I'm not sure if we should compare the `title` though.