recognize IE11 as MSIE, fix #460

Detect IE11's new user agent based on:

* http://blogs.msdn.com/b/ieinternals/archive/2013/09/21/internet-explorer-11-user-agent-string-ua-string-sniffing-compatibility-with-gecko-webkit.aspx
* http://msdn.microsoft.com/en-us/library/ie/ms537503(v=vs.85).aspx#UATokenRef