Add x11 backend for compositor

This still needs all the bells and whistles from the egl-kms mesa branch,
but it makes it a lot easier to work on wayland.

event-loop.c

@@ -342,6 +342,7 @@ wl_event_source_idle_remove(struct wl_event_source *source)
 		(struct wl_event_source_idle *) source;
 
 	wl_list_remove(&idle_source->link);
+	free(source);
 
 	return 0;
 }