[MLton] PDF docs patch

[Stephen Weeks]

> Here is a patch I have floating around from Fedora. It installs
> documentation in PDF format by default instead of PS.gz format. Maybe
> this is worth having upstream?

I'd prefer to ship the docs in PDF too.  Making the pdfs currently
requires pdflatex -- I don't see a Debian package for that, and we
need someway to build on Debian.  Does anyone know where pdflatex is,
or some equivalent on Debian?