Don't generate the mod???.idx file if it wasn't requested with the new command
\makemodindex.
Change the format of mod???.idx to match that of "normal" .idx files. This
lets us use makeindex for it and not need a special script.
now requires LaTeX2HTML 98.1p1 or newer (& and is still in progress).
This means that doing things to change the formatting of the manuals (at the
"normal user" level, like A4 paper), can happen in just one place, rather
than in each document file.