bug#24218: 25.1.50; server-name, server-socket-dir and daemon start through, systemd socket

[Eli Zaretskii <eliz@gnu.org>]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sun, 7 Jan 2018 13:55:04 -0800
> Cc: 24218@debbugs.gnu.org, Vladimir Lomov <lomov.vl@gmail.com>
> 
> Matthew proposed a patch for this here:
> 
> https://lists.gnu.org/r/emacs-devel/2017-12/msg00903.html
> 
> which I am attaching in git form (see first attached patch). I also 
> propose the second attached patch as a followup. It makes some of the 
> newly-added features "private" (since they don't seem to be generally 
> useful) and moves the low-level initialization code from emacs.c to 
> process.c which is a more-natural home for it.

Thanks.  I'm not an expert on this stuff, so I have only minor
comments:

  . Please update the :version tag of server-name, to reflect the fact
    that its default value changes
  . This needs a NEWS entry, and I think the description of
    server-name in the manual should be updated to mention this
    facility
  . internal--external-sockname should be documented in the ELisp
    manual (a better name that doesn't use both "internal" and
    "external" will be appreciated)