bug#62524: Support displaying all package maintainers

[Jonas Bernoulli <jonas@bernoul.li>]

[ I am re-sending this message because the MDS refused to deliver
  the previous iteration.

  Stefan, your reply contained a header "Cc: ??@debbugs.gnu.org". ]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Even once all ELPAs have been updated to include `:maintainers', they
>> have to continue to also include `:maintainer', for the benefit of
>> older versions of this function / package.el / Emacs.
>
> We could drop `:maintainer` within a few years, tho: this info is not
> super-important and it would impact only users of older Emacsen.

That's the plan.

>> To avoid this duplication, `package' would have to be distributed on
>> GNU ELPA as a "core" package.
>
> That still wouldn't help those users who didn't upgrade their built-in
> `package.el`.

I hope that we can eventually not only make Package available on GNU
Elpa, but also get users of older Emacs releases to update to that
version, see 87tty24ap2.fsf@bernoul.li

> Other than that: OK with me.

So should I go ahead and install this now (on master, I assume)?

Once that is done, I'll update the elpa-admin equivalent for Melpa.  I
plan to only include :maintainers in archive-contents if there actually
are multiple maintainers.  That way there is less duplicated data, and
I recommend you do the same in elpa-admin.

Oh, and the comment you added to package-buffer-info in 4e6f98cd505ed56
is wrong; shall I just replace "single string" with "single cons-cell"?

     Cheers,
     Jonas