[Dovecot] Pre-rev1 compatibility

[Hans Werner Strube]

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.