Instead of having an assertion failure with a message of dubious
usefulness, we should probably use a more verbose warning explaining
what is the problem and what might be the cause.
* clutter/clutter-id-pool.c: (clutter_id_pool_free):
Use g_slice_free not g_free.
* clutter/clutter-main.c: (_clutter_do_pick):
Dont 'over read' the framebuffer when picking (#839, Neil Roberts)
contained data structure.
* clutter/clutter-id-pool.[ch]: new files.
* clutter/Makefile.am: added clutter-id-pool.[ch]
* clutter/clutter-private.h: use a ClutterIDPool instead of GArray and
GSList to keep track of the reusable ids.
* clutter/clutter-actor.c: moved id pool logic away.
* clutter/clutter-main.c: simplified id pool creation/finalization.
