EVBACKEND_POLL
if (EV_USE_POLL ) flags |= EVBACKEND_POLL;
flags &= ~EVBACKEND_POLL; /* poll is based on kqueue from 10.5 onwards */
flags &= ~EVBACKEND_POLL; /* poll return value is unusable (http://forums.freebsd.org/archive/index.php/t-10270.html) */
if (!backend && (flags & EVBACKEND_POLL )) backend = poll_init (EV_A_ flags);
if (backend == EVBACKEND_POLL ) poll_destroy (EV_A);
return EVBACKEND_POLL;