bug#46979: Allow setting Man-default-entry via Local Variables

[Eli Zaretskii <eliz@gnu.org>]

> From: 積丹尼 Dan Jacobson <jidanni@jidanni.org>
> Cc: mardani29@yahoo.es,  46979@debbugs.gnu.org
> Date: Tue, 09 Mar 2021 22:24:20 +0800
> 
> >>>>> "EZ" == Eli Zaretskii <eliz@gnu.org> writes:
> 
> EZ> OK, but why do you insist on doing this via file-local variables?
> 
> Because certainly the people who make the alists will probably think
> that crontab(1) is the man page people editing crontabs want to see,
> but individual programmer Williams wants to see crontab(5) usually.
> But wait! Not always. For his other cron page he more often wants to see
> cron(8), and even crontab(1posix). So you never know.

But Mr Williams does know!  And the alist can be modified exactly like
the local-vars section in a file.

With your suggestion, by default Emacs will be none the wiser, because
wizard jidanni didn't visit every Mr Williams out there and offered
them his services of adding the local-vars section to every obscure
file they might have on their disk.  Including flippant(1),
fartsburg(7) and whatnot.

A good tool shines when it does DWIM without any tinkering.  The
"alist solution" has much higher chances of doing a large part of the
job, so insisting on not doing anything and leaving everything to the
user's tinkering makes little sense to me.