osx: Improve the event loop

Implementation of event loop which works with GLib events, native OS X
events and Clutter events.

The event loop source code comes from the equivalent code in the Quartz
GDK backend from GTK+ 2.22.1, which is LGPL v2.1+ and thus compatible
with Clutter's licensing terms.

The code has been tested with libsoup, which did not work before together
with Clutter.

Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>

http://bugzilla.clutter-project.org/show_bug.cgi?id=2490

clutter/clutter-debug.h

@@ -24,7 +24,8 @@ typedef enum {
   CLUTTER_DEBUG_MULTISTAGE          = 1 << 13,
   CLUTTER_DEBUG_ANIMATION           = 1 << 14,
   CLUTTER_DEBUG_LAYOUT              = 1 << 15,
-  CLUTTER_DEBUG_PICK                = 1 << 16
+  CLUTTER_DEBUG_PICK                = 1 << 16,
+  CLUTTER_DEBUG_EVENTLOOP           = 1 << 17
 } ClutterDebugFlag;
 
 typedef enum {