[latexrefman] \write, \message, \wlog, \write18

[Karl Berry]

I think the description of \write and friends is good. I just committed
a few small tweaks. Perhaps most notable is adding \immediate to the
\write and \closeout in the first example. It didn't make sense to me to
have the \openout be \immediate and not the others. (Alternatively, they
could all be non-immediate, but ...) Let me know if I'm missing
something.

Also, in the example
  before\message@{One Two@}\message@{Three@} \message@{Four^^JI@}

I thought it would be better to omit the space after three:
  before\message@{One Two@}\message@{Three@}\message@{Four^^JI@}

because otherwise the reader has to realize that that (interword) space
and the one from the end of line (after the Four) are getting combined
into one, which seemed like an unnecessary complication.

Hope I didn't mess anything up ... --thanks, karl.

P.S. I've found it's useful to make an explicit ChangeLog entry at each
release. That way it's possible to review the ChangeLog and easily know
which changes are in which releases.