fixes #687 POLLHUP is problematic on macOS too...
fixes #687 POLLHUP is problematic on macOS too...

Basically, we can ignore EV_EOF, as we wind up still alerting
the corresponding events.  EV_ERROR we still treat as HUP.

(The EV_EOF was responsible for prematurely closing the socket
and aborting transactions while there was still data in the socket
buffers.)

nanomsg/nng,nanomsg/nng,nanomsg/nng,nanomsg/nng