Fixes for Calendar widget

Miscellaneous fixes from review:

- Distribute calendar.js and the interactive test
- Make the pointless protection against leap seconds actually work
  by starting in the middle of the day so that forward/back always
  move a day.
- Use a variable instead of an inline '8' to know where to start
  when removing old day actors.
- Remove a stray comment from the test

https://bugzilla.gnome.org/show_bug.cgi?id=596432

js/ui/panel.js

@@ -518,6 +518,10 @@ CalendarPopup.prototype = {
         this.calendar = new Calendar.Calendar();
         this.actor.add(this.calendar.actor);
 
+        // Directly adding the actor to Main.chrome.actor is a hack to
+        // work around the fact that there is no way to add an actor that
+        // affects the input region but not the shape.
+        // See: https://bugzilla.gnome.org/show_bug.cgi?id=597044
         Main.chrome.actor.add_actor(this.actor);
         Main.chrome.addInputRegionActor(this.actor);
         this.actor.y = (panelActor.y + panelActor.height - this.actor.height);