顶号下线：新登录挤掉旧会话

local function onLogin(actor, acc)
    -- 不查旧会话，双开两地同时在线
end

local ONLINE = {}
local function onLogin(actor, acc)
    local old = ONLINE[acc]
    if old and old ~= actor then
        kick(old)                   -- 顶掉旧会话
        sendmsg(old, 1, "账号在别处登录，您已被顶下线")
    end
    ONLINE[acc] = actor
end
local function onLogout(actor, acc)
    if ONLINE[acc] == actor then ONLINE[acc] = nil end
end