The URLs of the form `help://man/<section>/<page>` link to another help
page inside the help application. All previous relative page links are
replaced by this new form. This doesn't change any behavior but it looks
much nicer :^)
Note that man doesn't handle these new links, but the previous relative
links didn't work either.
I can't write these manpages ad-hoc, and in most cases I don't want to
remove the link because it is justified. The hope is that with this
FIXME in place, there is more motivation to write these manpages for
someone who knows enough about them. Or at least we will introduce fewer
dead links in the future, making Help more useful.