add new prototype mailbox_recent_count

 /* GNU mailutils - a suite of utilities for electronic mail
-   Copyright (C) 1999, 2000 Free Software Foundation, Inc.
+   Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU Library General Public License as published by
@@ -58,6 +58,7 @@ extern int mailbox_set_folder     __P ((mailbox_t, folder_t));
 extern int mailbox_get_message    __P ((mailbox_t, size_t msgno, message_t *));
 extern int mailbox_append_message __P ((mailbox_t, message_t));
 extern int mailbox_messages_count __P ((mailbox_t, size_t *));
+extern int mailbox_recent_count   __P ((mailbox_t, size_t *));
 extern int mailbox_expunge        __P ((mailbox_t));
 
 /* Update and scanning.  */