2006-06-16  Matthias Clasen  <mclasen@redhat.com>

	* gtk/gtkprintoperation-unix.c:
	* gtk/gtkprintbackend.c: Move the registration of the
	gtk-print-preview-command setting from gtkprintbackend.c to
	gtkprintoperation-unix.c, to make sure it is registered before
	the first use. Also, document the two settings.