Use the environment context in the menu. Remove the commands
"default" and "timeout", and use variables instead.
* normal/menu.c: Include grub/env.h.
(print_entry): Cast TITLE to silence gcc.
(get_timeout): New function.
(set_timeout): Likewise.
(get_entry_number): Likewise.
(run_menu): Use a default entry, a fallback entry and a timeout
in the environment variables "default", "fallback" and
"timeout". Also, tweak the default entry if it is not within the
current menu entries.
(grub_menu_run): Use a fallback entry in the environment variable
"fallback".
* normal/main.c (read_config_file): Do not initialize
NEWMENU->DEFAULT_ENTRY, NEWMENU->FALLBACK_ENTRY or
NEWMENU->TIMEOUT.
(grub_normal_execute): Use a data slot to store the menu.