[tex-k] Reproducible builds using pdftex

[Karl Berry]

    Producing the document in a version that corresponds to the author's
    wish for the date the sources were last modified 

But that is not the author's wish, in theory.  If they use \today, by
definition they meant *today*, the day the document is being processed.

I certainly agree that most (though not all) authors using \today intend
"date of last source modification".  But then they should not use
\today.  \today means today.  That is what we are subverting with these
envvars.  This is why I think it should be considered a document bug and
(ha ha) in the fullness of time (sometime after the heat death of the
universe, no doubt) be eradicated.  -k