clutter-gtk: fix initialization order

Clutter-GTK must be initialized before Clutter. Clutter-GTK initializes
Clutter internally. And Clutter initialization can be called n-times. If
two or more Clutter initialization are just ignored.

GitHub: fix #274

Reported by mtasaka. Thanks!!!

clutter-gtk/lib/clutter-gtk.rb

@@ -43,9 +43,9 @@ class << self
         remove_method(:init)
         remove_method(:const_missing)
       end
-      Clutter.init(argv) if Clutter.respond_to?(:init)
       loader = Loader.new(self, argv)
       loader.load("GtkClutter")
+      Clutter.init(argv) if Clutter.respond_to?(:init)
     end
   end