Wait for user entry basing on presence of output rather than on errors.

	* include/grub/normal.h (grub_normal_get_line_counter): New proto.
	(grub_install_newline_hook): Likewise.
	* normal/main.c (GRUB_MOD_INIT): Call grub_install_newline_hook.
	* normal/menu.c (show_menu): Check line_counter to determine presence
	of output.
	* normal/term.c (grub_normal_line_counter): New variable.
	(grub_normal_get_line_counter): New function.
	(grub_install_newline_hook): Likewise.