Additional fixes for file notification

Additional fixes for file notification

* lisp/filenotify.el (top): Require 'cl when compiling.
(file-notify--event-watched-file): New defun.
(file-notify--rm-descriptor, file-notify-callback):
Handle case of several monitors running in parallel.

* test/automated/file-notify-tests.el
(file-notify--test-event-test): Simplify test.
(file-notify--test-with-events): Get rid of outer definition.
Check also results of tests performed in callbacks.
(file-notify-test02-events): No wrapping when calling
`file-notify-rm-watch'.  No special checking for callback tests.
(file-notify-test07-backup): Adapt expected events for gfilenotify.
(file-notify-test08-watched-file-in-watched-dir): Improve.