[latexrefman] latexmk as an alternative to write18

[Karl Berry]

    Still on node \write18, where sagetex is given as an example.

I don't see a need for the sagetex example, and just deleted it
(sorry, Jim).

    Personally, I find that using an appropriate latexmk configuration is
    both safer and simpler, 

I don't disagree in general, but I prefer not to mention latexmk, or any
other "front end" of whatever kind, in latex2e.texi, except perhaps in a
generic list mentioning that such things exist. They are, by definition,
not part of LaTeX itself. --thanks, karl.