bug#74616: 30.0.92; tmm always displays the *Completions* buffer

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> I think the automatic detection is a better default behavior, but
> maybe we could have a variable (not necessarily a defcustom) for users
> who would like to have the old behavior.
> Stefan, WDYT?

I often use the standard UI and I generally don't like this eagerness to
display *Completions*, so I'd either change the code not to auto-display
the buffer (what I have done locally) or at least offer a variable
for that.

So it seems like the war should have 3 settings: always show, never
show, and "guess" (tho maybe we can skip the "guess" option and let the
other completion UIs set the var to nil).


        Stefan