bug#16507: 24.3; systemd unit for a GNU Emacs daemon

[Philipp Moeller]

systemd provides an easy way to set-up a per-user Emacs daemon and there
are several unit files floating around the web. One that works is:

  /etc/systemd/system/emacs@.service
  ----------------------------------
  [Unit]
  Description=GNU Emacs: the extensible, self-documenting text editor
  
  [Service]
  Type=forking
  ExecStart=/usr/bin/emacs --daemon
  ExecStop=/usr/bin/emacsclient --eval "(progn (setq kill-emacs-hook 'nil) 
(kill-emacs))"
  Restart=always
  User=%i
  
  [Install]
  WantedBy=multi-user.target

It would be helpful to include this with the default GNU Emacs, so
users don't need to maintain their own files.

The above file would need some configuration through configure to set
the install path correctly and there should be an option to enable or
disable installing it via --with-systemd.