(perform_subtraction): New static function, extracted from
do_sub_recpt. Only send async-sub-recipient if the new argument want_async is true. (do_sub_recpt): Code simplified by creation of perform_subtraction(). New argument: want_async (see above). (do_delete_text): Tell do_sub_recpt that we don't want any async-sub-recipient messages. (sub_recipient): Tell do_sub_recpt to send async-sub-recipient messages.