bug#6204: vc-dir always splits the frame

[Stefan Monnier <monnier@iro.umontreal.ca>]

> "As a special case, if FRAME-PARAMETERS contains (same-window . t) ..."
> so should we now say
> "As another special case, if FRAME-PARAMETERS contains
> (other-window . t) ..."

We also have (same-frame . t), and we came to the conclusion at some
other point that we also want to have something like `nearby'
(i.e. other-window but close) or `near-minibuffer' (tho maybe `nearby'
is sufficient if near-minibuffer is only needed when the minibuffer is
the selected windows).

I feel like maybe these shouldn't be all separate parameters, but
instead we may want to have a single `where' parameter whose value could
then say `same-window', `other-window'.  OTOH we probably to be able to
specify some of the independently (I'm think mostly of `same-frame').

So maybe it should be split into `which-frame' which could be `same' or
`other' or nil, and then `where' which could be `same-window', or
`other-window', or `nearby', or nil.

Then we can even imagine in a distant future that the `other-frame' case
could pay attention to the `where' parameter to decide which other frame
to use and (if creating a new frame) where to place that frame.


        Stefan