Lua loader: support to load lua files in a encrypted zip file

功能：

使得Lua loader能够载入一个代码包，此代码包里的代码文件经过了字节码编译处理并打成zip包，并有可能经过了xxtea加密处理。
This static var is only used in the static function "lua_loadChunksFromZIP", and the function was exported to lua.