Improve filenotify-tests.el

Improve filenotify-tests.el

* src/inotify.c (Finotify_valid_p):
* src/kqueue.c (Fkqueue_valid_p):
* src/w32notify.c (Fw32notify_valid_p):
* src/gfilenotify.c (Fgfile_valid_p): Fix typo in docstring.
(Fgfile_monitor_name): New defun.
(syms_of_gfilenotify): Declare Sgfile_monitor_name.

* test/lisp/filenotify-tests.el	(file-notify--test-read-event):
New defun, derived from `file-notify--test-read-event-timeout'.
Replace all calls of `read-event' by this.
(file-notify--test-timeout): Fix docstring.
(file-notify--test-monitor): New defun.
(file-notify--deftest-remote): Do not bind
`file-notify--test-read-event-timeout' anymore.
(file-notify-test00-availability): Print also monitor, if existent.
(file-notify--test-with-events): Add an additional
`file-notify--test-read-event' call, in order to get it work
after `file-notify-add-watch'.  Remove special timeout for cygwin.
(file-notify-test02-events): Make a better check for cygwin.
(file-notify-test06-many-events): Improve event list for cygwin.
(file-notify-test08-watched-file-in-watched-dir): Add cygwin case.