loading message.el for two small functions

[Richard Stallman]

        * mail/smtpmail.el: Use with-current-buffer.
        (message-make-date, message-make-message-id): Autoload when needed.

message.el is almost 5000 lines.  It is very inefficient to load that
file just to get these two small functions.  Would you please copy and
rename the functions instead?

That will not only be more efficient, it will also make smtpmail.el
easier to read and understand on its own.