Show feedback notifications when the user is busy

Notifications that are created in response to direct user actions like
"is ready" or "'foo' has been removed from favorites" should always be
displayed even though the user has marked him/herself busy.

https://bugzilla.gnome.org/show_bug.cgi?id=662900

js/ui/windowAttentionHandler.js

@@ -39,6 +39,8 @@ const WindowAttentionHandler = new Lang.Class({
         let [title, banner] = this._getTitleAndBanner(app, window);
 
         let notification = new MessageTray.Notification(source, title, banner);
+        notification.setForFeedback(true);
+
         source.notify(notification);
 
         source.signalIDs.push(window.connect('notify::title', Lang.bind(this, function() {