* src/glade-builtins.[ch]: Added GLADE_TYPE_STOCK_IMAGE (and standard
	  pspec for it), this is stock items plus the additional "stock images"
	  from gtkstock.h (closing bug 353522).

	* src/glade-editor-property.c: recognize new stock image pspec type.

	* src/glade-gtk.c, widgets/gtk+.xml.in:
	  - Bulletproofed toolbar code wrt stock images (also use stock "images"
	    instead of items here)
	  - Use stock "images" for GtkImage
	  - GtkImage "type" property now defaults to "stock"
	  - GtkImage stock id now defaults to "gtk-missing-image"