don't let actions on a closed ZMQStream crash ioloop
don't let actions on a closed ZMQStream crash ioloop

adds _check_closed() to on_foo() calls.
dash-dash/pyzmq,yyt030/pyzmq,dash-dash/pyzmq,ArvinPan/pyzmq,swn1/pyzmq,caidongyun/pyzmq,yyt030/pyzmq,ArvinPan/pyzmq,Mustard-Systems-Ltd/pyzmq,swn1/pyzmq,swn1/pyzmq,ArvinPan/pyzmq,yyt030/pyzmq,Mustard-Systems-Ltd/pyzmq,caidongyun/pyzmq,caidongyun/pyzmq,Mustard-Systems-Ltd/pyzmq,dash-dash/pyzmq