Bug 1060694 - Next button stays active even after clearing the text fiel...

...ds during New Account setup
I prefer the older patch method of binding to formElem.addEventListener -- this allows it to work even if the controller for the form inserts new elements after first calling the FormNavigation.

This does mean it makes the click handler receive more clicks, but I believe returning early if the event.target is not a reset button is a lower cost. Only binding one event listener is less memory overhead than one per button element too.