Add warning for set_hwm.
Add warning for set_hwm.

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