Clean SendingQueuePool when the server is shutting down
Clean SendingQueuePool when the server is shutting down

chucklu/SuperSocket,chucklu/SuperSocket,fryderykhuang/SuperSocket,fryderykhuang/SuperSocket,ZixiangBoy/SuperSocket,ZixiangBoy/SuperSocket,fryderykhuang/SuperSocket,chucklu/SuperSocket,jmptrader/SuperSocket,ZixiangBoy/SuperSocket,jmptrader/SuperSocket,jmptrader/SuperSocket