bug#39138: 28.0.50; Add variables for shell command output buffer names

[Tino Calancha]

On Tue, 19 May 2020, Stefan Kangas wrote:

> Eli Zaretskii <eliz@gnu.org> writes:
>
> > > This seems to have stalled.  Is anyone still interested in this change,
> > > or should the bug be closed?
> >
> > It sounds like the best consensus we could have is to make defconsts
> > out of these strings, to avoid having many identical copies of them.
>
> Right.  Tino, could you take a look at that and see if it makes sense to
> send an updated patch?

TBH, I am not that much interested in this change (even if I opened it).
Since yesterday I am again w/ bug#39121 which provides more value.

Also, I have in my TODO list to open a bug for `iconify-frame', which 
gives me some problems in one of my laptops (under investigation).

Please, feel free to get ownership of the present bug if you find it 
useful, or close it as won't fix.