利用xmlhttp对象获取远程的数据，然后用二进制输出到客户浏览器，让客户下载数据,此例从某一远程服务器获取一个压缩包，并且输出到浏览器提供客户下载-Xmlhttp object the use of remote data access, and then use the binary output to the browser client to allow customers to download data, in this case from a remote server to ob