s3:pylibsmb: add notify() support

s3:pylibsmb: add notify() support

The operation is a bit different from others,
as results are returned in an async fashion.
It returns a request handle.

  notify_req = conn.notify(fnum=fnum,
                           buffer_size=0xffff,
                           completion_filter=libsmb.FILE_NOTIFY_CHANGE_ALL,
                           recursive=True)

  # ... do other operations on conn.*() ...

  changes = notify_req.get_changes(wait=False)
  # changes is likely to be None if no result arrived yet

  # ... do other operations on conn.*() ...

  changes = notify_req.get_changes(wait=True)
  # changes is a list of change dictionaries
  # each containing "name" (a string) and
  # "action" (an integer, e.g. libsmb.NOTIFY_ACTION_REMOVED)

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>