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

[Lars Ingebrigtsen]

Tino Calancha <tino.calancha@gmail.com> writes:

> IMO, the two strings, `*Shell Command Output*' and
> `*Async Shell Command*', deserve variables with their docstrings.

Skimming the thread, the rough consensus here was that this was a good
idea, but that these should be constants instead.  So I've applied the
patch to Emacs 28 and then adjusted the variable/constant bit.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no