Ajax on IE 7: Check native first

Well, apart from being pretty verbose, in the world of IE7 we should be invoking XMLHttpRequest() first and having the ActiveX control done only if window.XMLHttpRequest isn't around to play.

Well, apart from being pretty verbose, in the world of IE7 we should be invoking XMLHttpRequest() first and having the ActiveX control done only if window.XMLHttpRequest isn't around to play.