bug#6204: vc-dir always splits the frame

[Stefan Monnier]

> If the overriding case and the user option coincide in principle but the
> user option has additional values like in the foo-other-frame case with
> the user specifying certain frame parameters what shall we do?  Apply
> the frame parameters?  Should the additional argument also allow such
> frame parameters?  Should, as a rule, the potential argument's values be
> identic to the values allowed by the option?

Yes, I'm picturing the special arg as (conceptually) two alists, and
that we'd combine with the user's own setting via something like

  (append override-params
          (lookup special-display-regexps)
          default-params)


-- Stefan