bug#25781: Install misc documentation to /usr/share/doc/emacs-##

[Eli Zaretskii <eliz@gnu.org>]

> From: Glenn Morris <rgm@gnu.org>
> Date: Fri, 17 Feb 2017 22:24:24 -0500
> 
> The (file hierarchy) standard place for software to install
> miscellaneous (non-Info, non-man) documentation, examples files, etc on
> Unix systems is /usr/share/doc/package-version. In autoconf, this is the
> standard variable docdir, eg /usr/share/doc/emacs-25.1 .
> 
> On both Red Hat and Debian systems, I have several thousand directories
> in /usr/share/doc, but Emacs does not install anything there. IMO, much
> of the stuff that Emacs installs in /usr/share/emacs/25.1/etc belongs in
> /usr/share/doc/emacs-25.1. The exceptions would be any actual data files
> that Emacs needs at runtime (eg ps-prin0.ps).

I agree.  Can you propose a list of files that should be installed in
docdir?  If some of these files are accessed by Emacs features (e.g.,
NEWS), we will also have to change the corresponding code to access
them both in non-installed and installed Emacs.  (This is something
most, if not all, projects I built don't get right, btw.)

> In practical terms, this could be done by a special install rule that
> puts things from the existing etc/ source directory in the right place,
> or a new directory (sadly doc/misc is already taken) could be added to
> the source, and files moved there from etc/.

I'd prefer not to move files in the repository, as doing that runs
afoul of important Git features.

Thanks.