removed pointless 'flush' option from client
removed pointless 'flush' option from client

benjamg/zmqpp,chenwenbin928/zmqpp,benjamg/zmqpp,pin3da/zmqpp,kernelim/zmqpp,xaqq/zmqpp,sunkin351/zmqpp,kernelim/zmqpp,datasift/zmqpp,zeromq/zmqpp,xaqq/zmqpp,datasift/zmqpp,sunkin351/zmqpp,pin3da/zmqpp,chenwenbin928/zmqpp,zeromq/zmqpp