Bug 847032 - [email] IMAP only supports initially-SSL encrypted connections, STARTTLS upgrade not supported from unencrypted cleartext. r=asuth

Land https://github.com/asutherland/simplesmtp/pull/1 with one extra fix as part of the merge.  Specifically, mcav's tip commit allows a HELO bypass.  We want this landed before wake-up time for Cali, so this.