Fix automake warning on CLEANFILES
Fix automake warning on CLEANFILES

CLEANFILES is already defined, append the needed files.

GNOME/clutter-gst,GNOME/clutter-gst,GNOME/clutter-gst,skinkie/clutter-gst,lubosz/clutter-gst,GNOME/clutter-gst,ystreet/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst,lubosz/clutter-gst,lubosz/clutter-gst,ystreet/clutter-gst,ystreet/clutter-gst,skinkie/clutter-gst