(is_member_in): New static function.
(is_member_in_recpt): Use is_member_in to simplify code. (is_member_in_recpt_of): New static function. (is_member_in_linked_recpt): New static function. (interested_party): New static function. This also considers if the potential message recipient is a member of a recipient of a text that is linked to the text, via a misc-info or a aux-item. (send_async_sub_recipient): Use interested_party to determine if the asynchronous message should be sent. (send_async_deleted_text): Ditto. (send_async_new_text_old): Ditto. (send_async_new_text): Ditto. (send_async_add_recipient): Ditto. (text_read_access): Added const qualifiers.