Fix URL update when a transition triggered by popState is aborted

The bug is pretty easy to spot.

* Put this code in the BarRoute
```js
actions: {
  willTransition: function(transition) {
    transition.abort();
  }
}
```
* You transition from /foo to /bar
* You click the back button of the browser
* The transition is aborted and you are still in the bar route but
  the url has been update to /foo incorrectly.

The link-to helper handled this situation, but the transitions triggered by a
popState didn't.
Now then a transition is aborted the url previously poped is pushed again,
leaving the history unchanged.
The url flicks momentaneusly, but seems reasonable.

TODO:

* No idea how to test this.
* No idea if affects to other kind of Location handlers other than the
  HistoryLocation.