There's now a Forget History item in the Go menu which
	(after confirmation) forgets the history items in the Go
	menu and the back/forward chains of each Nautilus window.
	Afterwards, the Go menu's history list contains only locations
	currently being displayed.

	* src/nautilus-window.h: Changed back_list and forward_list
	from GSList * to GList * so I could use nautilus glist
	convenience functions (there's no efficiency issue with these
	small lists). Added prototypes for new functions
	nautilus_clear_back_list, nautilus_clear_forward_list, and
	nautilus_forget_history.

	* src/nautilus-window.c:
	(nautilus_window_clear_forward_list),
	(nautilus_window_clear_back_list): New functions that free and
	set to NULL the back & forward lists.
	(nautilus_window_destroy): Use nautilus_window_clear_back_list
	and nautilus_window_clear_forward_list instead of replicating code.
	(nautilus_window_back_or_forward),
	(nautilus_window_get_base_page_index): Replace "slist" with "list"
	(free_history_list): Set history_list variable to NULL in addition
	to freeing its contents.
	(nautilus_forget_history): New function, walks through all windows
	clearing out their back/forward lists, and throws away all of the
	history list except currently-displayed locations.

	* src/nautilus-window-manage-views.c: (handle_go_back),
	(handle_go_forward), (handle_go_elsewhere): Changed "slist"
	to "list" in various places; called new nautilus_clear_forward_list
	instead of replicating code.

	* src/nautilus-window-menus.c:
	(forget_history_if_confirmed): New function, calls nautilus_history_forget
	if user confirms via modeless dialog (because it would be a pain to
	accidentally choose this menu item and erase your history).
	(go_menu_forget_history_callback): New function used by new menu item,
	calls forget_history_if_confirmed.
	(nautilus_window_initialize_menus): Add "Forget History" item to Go menu.

	* src/nautilus-window-toolbars.c: (create_back_or_forward_menu):
	Replace "slist" with "list"

	* src/file-manager/fm-directory-view.c:
	(fm_directory_view_real_create_background_context_menu_items):
	Just clarified a comment.