Fix menu title instability bug.

	Fix menu title instability bug.

	* grub-core/commands/menuentry.c (options): New option --id.
	(grub_normal_add_menu_entry): New argument id. All users updated.
	(grub_cmd_menuentry): Handle --id.
	(grub_menu_init): Accept unknown arguments.
	* grub-core/normal/main.c (features): Add feature_menuentry_id and
	feature_menuentry_options.
	* grub-core/normal/menu.c (grub_menu_execute_entry): Use id for
	saved_entry.
	(get_entry_number): Match with id as well.
	* include/grub/menu.h (grub_menu_entry): New member id.
	* util/grub-mkconfig_lib.in (grub_get_device_id): New function.
	* util/grub.d/00_header.in: Define menuentry_id_option.
	* util/grub.d/10_hurd.in: Define id.
	* util/grub.d/10_illumos.in: Likewise.
	* util/grub.d/10_kfreebsd.in: Likewise.
	* util/grub.d/10_linux.in: Likewise.
	* util/grub.d/10_netbsd.in: Likewise.
	* util/grub.d/10_windows.in: Likewise.
	* util/grub.d/20_linux_xen.in: Likewise.
	* util/grub.d/30_os-prober.in: Likewise.