* src/ntl-window-msgs.c (nautilus_window_update_internals): Handle
	freeing of window->ni in a fancier way to avoid double-free
	problems which were causing crashes after some amount of view
	switching and navigation. It might leak memory but it's the only
	obvious way to avoid crashing.
	* src/ntl-window.c (nautilus_window_destroy): Likewise to avoid
	crashing on exit.
	* src/ntl-window.h (Nautilus_NavigationInfo_free): Prototype this
	function.