[Exim] Small bug in the spec.txt

Hi!

spec.txt:

While running an ACL at the time of an SMTP RCPT command, $message_size
contains the size supplied on the MAIL command, or zero if no size was
given.

Really, $message_size is "-1" if no size was given.

Btw, how can I differ SMTP and ESMTP on helo/ehlo phase?
$received_protocol is "smtp" in the both cases.

--
                                Lucky carrier,
                                                  Pavel.