handle process shutdown a bit better
handle process shutdown a bit better

in the garbage collector

avoids some exceptions during interpreter shutdown errors
swn1/pyzmq,dash-dash/pyzmq,dash-dash/pyzmq,dash-dash/pyzmq,Mustard-Systems-Ltd/pyzmq,ArvinPan/pyzmq,yyt030/pyzmq,swn1/pyzmq,ArvinPan/pyzmq,caidongyun/pyzmq,ArvinPan/pyzmq,Mustard-Systems-Ltd/pyzmq,swn1/pyzmq,caidongyun/pyzmq,caidongyun/pyzmq,yyt030/pyzmq,Mustard-Systems-Ltd/pyzmq,yyt030/pyzmq