add socket.disconnected(), used by socketchannle. see #715

lualib/http/httpc.lua

@@ -104,17 +104,13 @@ function httpc.request(method, host, url, recvheader, header, content)
 	if timeout then
 		skynet.timeout(timeout, function()
 			if not finish then
-				local temp = fd
-				fd = nil
-				socket.shutdown(temp)
+				socket.shutdown(fd)	-- shutdown the socket fd, need close later.
 			end
 		end)
 	end
 	local ok , statuscode, body = pcall(request, fd,method, host, url, recvheader, header, content)
 	finish = true
-	if fd then	-- may close by skynet.timeout
-		socket.close(fd)
-	end
+	socket.close(fd)
 	if ok then
 		return statuscode, body
 	else