Add "precision" to boxpointer alignment

Allows the boxpointer arrow to be at a fixed percentage of the bubble

https://bugzilla.gnome.org/show_bug.cgi?id=642031

js/ui/dateMenu.js

@@ -56,7 +56,7 @@ DateMenuButton.prototype = {
         //this._eventSource = new Calendar.FakeEventSource();
         this._eventSource = new Calendar.EvolutionEventSource();
 
-        PanelMenu.Button.prototype._init.call(this, St.Align.START);
+        PanelMenu.Button.prototype._init.call(this, 0.0);
 
         this._clock = new St.Label();
         this.actor.set_child(this._clock);