Support for filesystem notifications on MS-Windows.

Support for filesystem notifications on MS-Windows.

 src/w32proc.c (sys_select): If drain_message_queue returns non-zero,
 and this is a TTY frame, signal the caller that keyboard input is
 available.
 src/w32xfns.c (drain_message_queue): Now returns an int: an
 indication whether any WM_EMACS_FILENOTIFY messages were found in
 the queue.
 src/w32inevt.c (handle_file_notifications): New function.
 (w32_console_read_socket): Call it to process file notifications.
 src/w32console.c (initialize_w32_display): Record the main thread ID
 in dwMainThreadId.
 src/deps.mk (inotify.o): New dependency list.
 src/Makefile.in (SOME_MACHINE_OBJECTS): Add w32notify.o.
 src/w32term.h (WM_EMACS_FILENOTIFY): New custom message.
 (WM_EMACS_END): Bump value by 1.
 (notification_buffer_in_use, file_notifications)
 (notifications_size, notifications_desc): Declare.
 (w32_get_watch_object, lispy_file_action, globals_of_w32notify):
 Add prototypes.
 src/w32term.c (lispy_file_action, queue_notifications): New functions.
 (syms_of_w32term) <Qadded, Qremoved, Qmodified, Qrenamed_from>
 <Qrenamed_to>: New symbols.
 (w32_read_socket): Handle the WM_EMACS_FILENOTIFY message.
 src/w32notify.c: New file, implements file event notifications for
 MS-Windows.
 src/w32fns.c (w32_wnd_proc): Handle the WM_EMACS_FILENOTIFY message
 by posting it to the w32_read_socket queue.
 src/termhooks.h (enum event_kind) [HAVE_NTGUI]: Support
 FILE_NOTIFY_EVENT.
 src/makefile.w32-in (OBJ2): Add $(BLD)/w32notify.$(O).
 (GLOBAL_SOURCES): Add w32notify.c
 ($(BLD)/w32notify.$(O)): New set of dependencies.
 src/lisp.h (syms_of_w32notify) [WINDOWSNT]: Add prototype.
 src/keyboard.c (kbd_buffer_get_event) [WINDOWSNT]: Handle
 FILE_NOTIFY_EVENT.
 (syms_of_keyboard) [HAVE_NTGUI] <Qfile_notify>: New symbol.
 (keys_of_keyboard) [WINDOWSNT]: Bind file-notify to
 w32notify-handle-event by default.
 src/emacs.c (main) [WINDOWSNT]: Call globals_of_w32notify and
 syms_of_w32notify.

 lisp/subr.el (w32notify-handle-event): New function.
 (inotify-handle-event): Doc fix.

 lib-src/makefile.w32-in (obj): Add w32notify.o.  Add missing X and Unix
 sources.