Prevent emacsclient errors when Emacs is compiled without X support.

Prevent emacsclient errors when Emacs is compiled without X support.

* lisp/frame.el (make-frame-on-display): Protect condition on
  x-initialized when x-win.el is not loaded.

* lib-src/emacsclient.c (main): Handle -window-system-unsupported
  command.  Doc update.

* lisp/server.el (server-process-filter): Don't try to create an X frame
  when Emacs does not support it.  Improve logging.

* lisp/server.el (server-send-string): New function.
  (server-handle-suspend-tty, server-process-filter): Use it.

* lisp/server.el (server-process-filter, server-unquote-arg)
  (server-quote-arg): Doc updates.

git-archimport-id: lorentey@elte.hu--2004/emacs--multi-tty--0--patch-286