own patch [#27752] Python Callback (Scriptlink functionality)

Python:
 * adds bpy.app.handlers which contains lists, each for an event type:
   render_pre, render_post, load_pre, load_post, save_pre, save_post
 * each list item needs to be a callable object which takes 1 argument (the ID).
 * callbacks are cleared on file load.

Example:
 def MyFunc(scene): print("Callback:", data)
 bpy.app.handlers.render_post.append(MyFunc)

C:
 * This patch adds a generic C callback api which is currently only used by python.
 * Unlike python callbacks these are not cleared on file load.

source/blender/blenlib/CMakeLists.txt

@@ -52,6 +52,7 @@ set(SRC
 	intern/DLRB_tree.c
 	intern/boxpack2d.c
 	intern/bpath.c
+	intern/callbacks.c
 	intern/cpu.c
 	intern/dynlib.c
 	intern/edgehash.c