Transitions which are aborted by an onBefore hook should not supersede other pending transitions

[00dani]

Currently a transition will always supersede any transitions that started before it - unfortunately, this includes transitions which never actually started themselves, due to being interrupted by an onBefore hook. For example, I wrote the following simple onBefore hook to prevent several clicks on the same ui-sref from "stacking up":

    mod.config(function($transitionsProvider) {
        let prevTarget = undefined;
        $transitionsProvider.onBefore({}, function(trans) {
            const target = trans.targetState().toString();
            if (prevTarget && target === prevTarget) return false;
            prevTarget = target;
        }, {priority: 9999});
    });

If you click the ui-sref several times, only the first transition will attempt to fetch its resolve data (as desired), with all later transitions immediately being aborted. However, once all resolve data have been retrieved, the first transition is also cancelled since other transitions were attempted.

Since onBefore is meant to be invoked before the transition even begins, it should be able to intercept and throw away unwanted transitions entirely, without having them interrupt other operations.