SMTP extended error codes stored in $smtp->error
Added HELO/EHLO reply parsing. Corresponding get methods: getServerExtensions(), getAuthAllowed(), getTLSAllowed()
Auth method selection added, according to STMP extensions list
A little bugfix
$helo_rply recovered. SMTP extension methods reconsidered (refer to comment)
Merge pull request #311 from heronman/master

A bugfix in SMTP::authenticate, plus some improvements