Fixed bug in ioloop.py when poll raises ETERM.
Fixed bug in ioloop.py when poll raises ETERM.

When a zeromq Context is closed, zmq_poll will return ETERM.
In this case, the ioloop should exit and stop.

swn1/pyzmq,yyt030/pyzmq,swn1/pyzmq,yyt030/pyzmq,yyt030/pyzmq,caidongyun/pyzmq,dash-dash/pyzmq,Mustard-Systems-Ltd/pyzmq,dash-dash/pyzmq,Mustard-Systems-Ltd/pyzmq,ArvinPan/pyzmq,dash-dash/pyzmq,swn1/pyzmq,Mustard-Systems-Ltd/pyzmq,caidongyun/pyzmq,caidongyun/pyzmq,ArvinPan/pyzmq,ArvinPan/pyzmq