Fixed some problems with callbacks that are left around after
	the object is destroyed.

	* src/nautilus-window-manage-views.h:
	* src/nautilus-window-manage-views.c:
	(viewed_file_changed_callback): Changed to be a normal callback,
	not a "connect_object" callback, and simplified the logic.
	(cancel_viewed_file_changed_callback): Added a function to cancel
	the callback, which is needed both when the window is destroyed
	and when the viewed file changes.
	(update_for_new_location): Cancel the old callback before setting
	up the new one so we don't leave behind callbacks for old locations.
	Also use the new nautilus_window_set_viewed_file function so the
	callbacks set up in nautilus-window.c can be managed properly.
	(free_location_change): Moved part of
	nautilus_window_free_load_info in here. This function frees all
	the stuff that's used in the location change process; shared by
	destroy and "cancel" code. Also fixed a bug where it wouldn't free
	the "erro...