* src/glade-project.c: Fixed broken resource pool & wrote some doc.
	  Now save the "<required lib="..."/> catalog requirements to the
	  glade file and complain when loading glade files that demand
	  unavailable catalogs.

	* src/glade-widget-class.[ch]: Added widget_class->catalog

	* src/glade-catalog.[ch]: Added glade_catalog_is_loaded (), call
	  gwc_new with catname arg.

	* src/glade-parser.c: Added glade_util_ui_message error messaging
	  when having errors loading glade files.

	* src/glade-project-window.c: Removed redundant error message.