generate darwin/platform.hpp on 10.6
generate darwin/platform.hpp on 10.6

removes TCP_KEEPCNT and TCP_KEEPINTVL from bundled libzmq, which are new on 10.8 or 10.9.
Mustard-Systems-Ltd/pyzmq,yyt030/pyzmq,ArvinPan/pyzmq,caidongyun/pyzmq,ArvinPan/pyzmq,caidongyun/pyzmq,swn1/pyzmq,caidongyun/pyzmq,yyt030/pyzmq,Mustard-Systems-Ltd/pyzmq,swn1/pyzmq,yyt030/pyzmq,ArvinPan/pyzmq,dash-dash/pyzmq,dash-dash/pyzmq,dash-dash/pyzmq,Mustard-Systems-Ltd/pyzmq,swn1/pyzmq