poll() revents are flags, and the lua module tests for equality...
Obviously this has been working merely by accident given that a remote
host resetting a connection generates only POLLIN, and neither POLLHUP
nor POLLERR.

lua doesn't support bitwise operators so this is the simplest way.
(cherry picked from commit ce00244d121cfba2bbbc5065fcd3a6eb84bbba6c)
Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>