Update "fetchmail" and "fetchmailconf" package to version 6.3.21.

Update "fetchmail" and "fetchmailconf" package to version 6.3.21.
Changes since version 6.3.20:
- The IMAP client no longer inserts NUL bytes into the last line of a
  message when it is not closed with a LF or CRLF sequence. Reported
  by Antoine Levitt.  As a side effect of the fix, and in order to
  avoid a full rewrite, fetchmail will now CRLF-terminate the last
  line fetched through IMAP, even if it is originally not terminated
  by LF or CRLF. This bears no relevance if your messages end up in
  mbox, but adds line termination for storages (like Maildir) that do
  not require that the last line be LF- or CRLF-terminated.