ensure event listener is activated (hooks)

The OS X delegate listener for an event is only activated if the
`on` call is made for the event id.
This is an optimization to prevent flooding the application with
events that the application does not actually care about.
The `impl.on` call is what activates the response handler for the
event in question.  This logic was missing in the RegisterHooks()
function but is present in the `On()` function.  In the case of using
`On()` first followed by `RegisterHooks()` things work correctly.

v3/pkg/application/application.go

@@ -397,6 +397,9 @@ func (a *App) RegisterHook(eventType events.ApplicationEventType, callback func(
 		callback: callback,
 	}
 	a.applicationEventHooks[eventID] = append(a.applicationEventHooks[eventID], thisHook)
+	if a.impl != nil {
+		go a.impl.on(eventID)
+	}
 
 	return func() {
 		a.applicationEventHooksLock.Lock()