* src/ntl-window.c, src/ntl-window.h: store zoom_control object in
	the window.

	* src/nautilus-zoomable-frame-svr.c: New file; implement CORBA
	server for Nautilus::ZommableFrame interface.
	* src/ntl-view-private.h: prototypes for shared stuff needed to make
	this work.
	* src/ntl-view.c: Attach a Nautilus::ZoomableFrame interface to
	the Nautilus::ViewFrame.

	* libnautilus/nautilus-gtk-extensions.h,
	libnautilus/nautilus-gtk-extensions.c
	(nautilus_gtk_marshal_NONE__DOUBLE): New function.