bug#6204: vc-dir always splits the frame

[martin rudalics]

> The downside to adding such parameters in a case where you modify existing
> functions (esp. if used heavily in existing code) is that it can make it 
harder
> for 3rd-party code to take advantage of the new feature and still work with
> older versions that do not have the new parameters.

I suppose that re-using the `other-window' argument of `display-buffer'
as Juri proposed will handle the problem you describe.

martin