Cherry-picked change from #3063
Cherry-picked change from #3063

jeremiahyan/AFNetworking,BohemianCoding/AFNetworking,kiurentu/AFNetworking,NextThought/AFNetworking,michal-olszewski/AFNetworking-CustomCallbacks,OmarPedraza/AFNetworking,wangxiaoxiang/AFNetworking,michal-olszewski/AFNetworking-CustomCallbacks,dake/AFNetworking,donholly/AFNetworking,kevin-zqw/AFNetworking,kiurentu/AFNetworking,dilumn/AFNetworking