[Dovecot] Pre-rev1 compatibility

What about adding some compatibility for pre-rev1 IMAP4 clients which are still around (e.g., CDE dtmail, even in Solaris 10)? Especially, the understanding of command FETCH message (... RFC822.HEADER.LINES (parameters)) instead of FETCH message (... BODY.PEEK[HEADER.FIELDS (parameters)]) (with correspondingly changed replies) would be desirable and shouldn't be too difficult to implement.