Support daemon mode on MS-Windows (bug#19688)

Support daemon mode on MS-Windows (bug#19688)

 src/emacs.c <w32_daemon_event> [WINDOWSNT]: New global var.
 (main) [WINDOWSNT]: Initialize it to NULL.  Create the event to
 signal clients we are ready for connections.
 (Fdaemon_initialized): Use DAEMON_RUNNING.
 [WINDOWSNT]: MS-Windows specific code to signal clients we are
 ready for connections.
 src/lisp.h (DAEMON_RUNNING): New macro, encapsulates Posix and
 MS-Windows conditions for running in daemon mode.
 src/minibuf.c (read_minibuf): Use DAEMON_RUNNING.
 src/keyboard.c (kbd_buffer_get_event): Use DAEMON_RUNNING.
 src/dispnew.c (init_display) [WINDOWSNT]: Initialize frames/terminal
 even in daemon mode.

 nt/inc/ms-w32.h (W32_DAEMON_EVENT): New macro.

 lib-src/emacsclient.c (decode_options) [WINDOWSNT]: Don't reject empty
 arguments for --alternate-editor.
 (print_help_and_exit) [WINDOWSNT]: Don't refrain from advertising
 empty arguments for --alternate-editor.
 (start_daemon_and_retry_set_socket) [WINDOWSNT]: MS-Windows
 specific code to start Emacs in daemon mode and wait for it to be
 ready for client connections.

 lisp/server.el (server-process-filter): Force GUI frames on
 MS-Windows in daemon mode, even if a TTY frame was requested.
 lisp/frameset.el (frameset-keep-original-display-p): Don't assume
 windows-nt cannot be in daemon mode.
 lisp/frame.el (window-system-for-display): Don't assume windows-nt
 cannot be in daemon mode.