cIOS设备连接到WiFi时 会发送一个HTTP请求到这个页面：
http://www.apple.com/library/test/success.html
HTTP请求：
GET /library/test/success.html HTTP/1.0
Host: www.apple.com
User-Agent: CaptiveNetworkSupport/1.0 wispr
Connection: close
相关的帖子：
http://stackoverflow.com/questions/3615147/how-to-create-wifi-popup-login-page
http://blog.erratasec.com/2010/09/apples-secret-wispr-request.html#.VaUMdc_vOSo
https://bugzilla.mozilla.org/show_bug.cgi?id=562917
https://code.google.com/p/chromium/issues/detail?id=185087
