Config(8) dependency checking - first patches

[Matt Emmerton]

> : Notes and patches against 7-CURRENT are at
> : http://www.gsicomp.on.ca/projects/freebsd/configdep.html.
>
> How would you encode ed's dependencies?  The ed driver only depends on
> mii when built with pccard enabled.

I suspected that conditional dependencies would be neccessary, but didn't
have any examples.
Now I do.  Thanks!

--
Matt Emmerton