bug#3717: M-x man completion

[Kevin Ryde]

Juri Linkov <juri@jurta.org> writes:
>
>   Possible completions are:
>   lib (3erl)
>   lib (3perl)

If you complete from "li" it gives "lib (", which will make man error
out.  I insert a bare "lib" for such cases so that completion stops
without the "(" for whatever is man's default page for "lib".  You may
have seen the "chmod" example in my code.

I also put in stuff like "3erl lib", since you can enter it like that to
man, and it can be easier to give the section first then complete among
pages in the section, as opposed to a section suffix.

That latter probably doesn't cooperate with Stefan's prefix-based cache
thing as it stands.  But I found it better to cache all page names once,
because a "-k" run is pretty much as slow asking for a few matches as
many.

I did say there was lots of things I've already been through for
friendliness and features!  :-)