bug#16407: Info-directory-list should always put this Emacs's info direc first

[Eli Zaretskii <eliz@gnu.org>]

> From: Glenn Morris <rgm@gnu.org>
> Date: Fri, 10 Jan 2014 00:46:39 -0500
> 
>    Therefore, the directory of Info files that come with Emacs normally
>    should come last (so that local files override standard ones), unless
>    Emacs is installed into a non-standard directory. In the latter case,
>    the directory of Info files that come with Emacs should be first in
>    this list.
> 
> I don't think this logic makes sense any more. I think the directory of
> Info files that come with Emacs should *always* be placed at the front of
> the result (even before INFOPATH entries).

That leaves system administrators no means of forcing a specific
version of Info manual to be found by default.  With INFOPATH taking
precedence, they can.

Also, Emacs comes with a few manuals that can have other versions from
elsewhere (like info.info or gnus.info).

> I assume the current logic dates from a time when it was thought likely
> that a site might want to customize the Emacs info pages. I don't think
> this happens any more. What I think does happen is people having
> multiple versions of Emacs installed.

Is this the only situation where the current arrangement doesn't DTRT,
or are there more?  If this is the only one, then you cannot solve it
successfully: the Info system simply doesn't support well the use case
where several different manuals have identical names.  The only way to
have the correct results is either by "C-u C-h i" and point Emacs to
the specific file name, or run all but one version uninstalled.

> In this case, I think Emacs version N should always display the info
> pages associated with version N.  So Emacs should always put its own
> info directory first.

What if the user installs newer versions of, say, Gnus or Org from
their respective repositories?