(smtpmail-cred-server, smtpmail-cred-port, smtpmail-cred-key)

(smtpmail-cred-server, smtpmail-cred-port, smtpmail-cred-key)
(smtpmail-cred-user, smtpmail-cred-cert, smtpmail-cred-passwd):
Defsubst instead of defmacro.
(smtpmail-intersection): Return value in reverse order.
(smtpmail-open-stream): Use stringp instead of string-to-list.
(smtpmail-open-stream, smtpmail-try-auth-methods): New functions,
separated from smtpmail-via-smtp.

(top level): Autoload starttls, mail-utils and rfc2104.
(smtpmail-smtp-service): Doc fix.  :type fix.
(smtpmail-debug-info): Doc fix.
(smtpmail-debug-verb, smtpmail-auth-credentials)
(smtpmail-starttls-credentials, smtpmail-auth-supported): New variables.
(smtpmail-deduce-address-list, smtpmail-send-it): Don't require
mail-utils (it is autoloaded).
(smtpmail-cred-server, smtpmail-cred-port, smtpmail-cred-key)
(smtpmail-cred-user, smtpmail-cred-cert, smtpmail-cred-passwd)
(smtpmail-find-credentials, smtpmail-intersection): New utility funs.
(smtpmail-via-smtp): Support STARTTLS, if binary is installed.
(smtpmail-via-smtp): Support AUTH.
(smtpmail-via-smtp): Use `smtpmail-debug-verb' to control VERB.