The event listener in Wicket.Ajax.ajax() should not return the value of attrs.ad (allowDefault)

Currently the event listeners registered in Wicket.Ajax.ajax() return the value of attrs.ad as a result.
This is wrong because this way the event propagation is effected.

event.preventDefault != event.stopPropagation

If the propagation has to be stopped then a before handler can do "Wicket.Event.stop(attrs.event)" where needed.