Must finish the STARTTLS command - especially what happens when it fails.

A quick TODO list follows.

• Upon success, will there be any response other than initiation of TLS/SSL communication?
• Upon failure, should probably differentiate between types of failure.
• Should the protocol restrict use of SSL1/2, as they are insecure?

To answer and/or comment upon all three bullets above...

• Yes, upon success there will be a positive single-line response from the server to indicate successful initiation of the TLS connection.
• The different types of failure will be implementation dependent (in other words, it's up to the server author how to implement error handling).
• The protocol will use TLS, not SSL, so this won't be an issue. - dave

Issue done.