replacement for @DATE@ from a TeX file containing a \date{...} mark
(such as texinputs/boilerplate.tex).

This will be used to re-write the html/index.html.in file instead of
a combination of grep, date, and sed -- this is more portable to non-Unix
platforms.

This solves part of the problem reported in SF patch #429611, but does
not use the suggested patch.