bug#54296: Add buffer-matching functionality

[Eli Zaretskii]

> Date: Thu, 16 Jun 2022 03:47:15 +0300
> Cc: 54296@debbugs.gnu.org, philipk@posteo.net, larsi@gnus.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> > Can you show a patch?
> 
> Please look at the patch attached to the very first message in this bug 
> report.
> 
> https://debbugs.gnu.org/cgi/bugreport.cgi?att=1;bug=54296;msg=5;filename=0001-Generalise-buffer-matching-from-project.el.patch
> 
> The function name has changed after discussion, but the docstring is 
> still relevant, and it mirrors 'project-kill-buffer-conditions'.

Other things changed as well, even in the doc string, and not just in
name changes.  Going back to the original patch makes little sense to
me.  So I'd still prefer to see an actual patch, before I tell whether
I'm okay with it.

In any case, if we will keep both major-mode and derived-mode
conditions in subr.el, let's at least document that derived-mode
should be preferred where it can do the job, and major-mode used only
where derived-mode will not DTRT.