(smtpmail-via-smtp): Recognize XVRB as a synonym for

(smtpmail-via-smtp): Recognize XVRB as a synonym for
VERB and XONE as a synonym for ONEX.

(smtpmail-read-response): Add "%s" to `message' calls to avoid
problems with percent signs in strings.

(smtpmail-read-response): Return all lines of the
response text as a list of strings.  Formerly only the first line
was returned.  This is insufficient when one wants to parse
e.g. an EHLO response.

Ignore responses starting with "0".  This is necessary to support
the VERB SMTP extension.

(smtpmail-via-smtp): Try EHLO and find out which SMTP service
extensions the receiving mailer supports.

Issue the ONEX and XUSR commands if the corresponding extensions
are supported.

Issue VERB if supported and `smtpmail-debug-info' is non-nil.

Add SIZE attribute to MAIL FROM: command if SIZE extension is
supported.

Add code that could set the BODY= attribute to MAIL FROM: if the
receiving mailer supports 8BITMIME.  This is currently disabled,
since doing it right might involve adding MIME headers to, and in
some cases reencoding, the message.