useragent.isIE should be updated to support IE9

Testing ACE on IE9, I noted that useragent.isIE returns "false" when it should be true. This causes a bug in the editor. Apparently the "\v"=="v" trick is no longer supported. From 

http://msdn.microsoft.com/en-us/library/ms537509%28v=vs.85%29.aspx

can we instead just check navigator.appName == 'Microsoft Internet Explorer'?
