Add SASL support MD5 : DIGEST-MD5 and CRAM-MD5
see authenticate in IMAPClient.pm

Tested  on
> The source imap server runs Cyrus imapd 1.6.22, 
> the destination one Cyrus imapd 2.1.12.
by Per Steinar Iversen  <PerSteinar.Iversen@adm.hio.no>

Add a list of well tested imap servers.