Added support for downgrading the SASL authentication mechanism when the
decoding of CRAM-MD5, DIGEST-MD5 and NTLM messages fails. This enhances
the previously added support for graceful cancellation by allowing the
client to retry a lesser SASL mechanism such as LOGIN or PLAIN, or even
APOP / clear text (in the case of POP3 and IMAP) when supported by the
server.
A failure during authentication, which is performed as part of the
CONNECT phrase (for IMAP, POP3 and SMTP) is considered by the multi-
interface as being closed prematurely (aka a dead connection). As such
these protocols cannot issue the relevant QUIT or LOGOUT command.
Temporarily fixed the test cases until we can fix this properly.
