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.
This is implemented in Line::Editor meaning not only the Shell will
respect it, but also js, Debugger etc.
Possible values are "ignorespace", "ignoredups" and "ignoreboth", as
documented in Shell-vars(7), for now.
The default value for the anon user (set in .shellrc) is "ignoreboth".
