Ajax: remove event dependency from the ajax module

Closes jquerygh-1695

Author: markelog

src/ajax/xhr.js

@@ -23,8 +23,9 @@ var xhrId = 0,
 
 // Support: IE9
 // Open requests must be manually aborted on unload (#5280)
-if ( window.ActiveXObject ) {
-	jQuery( window ).on( "unload", function() {
+// See https://support.microsoft.com/kb/2856746 for more info
+if ( window.attachEvent ) {
+	window.attachEvent( "onunload", function() {
 		for ( var key in xhrCallbacks ) {
 			xhrCallbacks[ key ]();
 		}