SF patch #461413 (Gerhard Häring): Add STARTTLS feature to smtplib

This patch adds the features from RFC 2487 (Secure SMTP
   over TLS) to the smtplib module:

   - A starttls() function
   - Wrapper classes that simulate enough of sockets and
     files for smtplib, but really wrap a SSLObject
   - reset the list of known SMTP extensions at each call
     of ehlo(). This should have been the case anyway.

Doc/lib/libsmtplib.tex

@@ -178,6 +178,14 @@ or may raise the following exceptions:
 \end{description}
 \end{methoddesc}
 
+\begin{methoddesc}{starttls}{\optional{keyfile, certfile}}
+Put the SMTP connection in TLS (Transport Layer Security) mode. All SMTP
+commands that follow will be encrypted. You should then call ehlo() again.
+
+If \var{keyfile} and \var{certfile} are provided, these are passed to the
+socket module's ssl function.
+\end{methoddesc}
+
 \begin{methoddesc}{sendmail}{from_addr, to_addrs, msg\optional{,
                              mail_options, rcpt_options}}
 Send mail.  The required arguments are an \rfc{822} from-address