Implement directory events

Implement directory events

* lisp/filenotify.el (file-notify-handle-event)
(file-notify-callback): Remove traces.

* src/kqueue.c: Include <sys/time.h>.
(kqueue_generate_event, kqueue_compare_dir_list): New functions.
(kqueue_callback): Use them.  Call kevent() with a zero timeout.
(Fkqueue_add_watch): Adapt docstring.  Support directory events.
Compute initial directory listing.  Close file descriptor in case
of errors.
(syms_of_kqueue): Declare Qcreate.