Fix bug aborting popstate

I hit the bug reported in this issue #5210 a few days ago. 

tl;dr
When you hit the back button and the transition is aborted, the url has already been updated is not rollbacked.

I've managed to fix it, but I have no clue about how to test it, because I would involve set some routes and play with the history. Seems almost an acceptance test to me.
* Transactions triggered with {{link-to}} do not trigger this.
* The forward button will probably trigger this too. I haven't checked but intuitively I think that if the transition aborts the url will be restored properly but the history will be corrupted.
* Calling `transitionTo` manually I'm not sure. Tomorrow I'll check it.

Any other way of triggering url updated other than these 3?