Fix #11757. IE 6/7 can't clean up circular DOM-JS refs.

Why? Because it's dumb. Verified with the case in the ticket.

src/support.js

@@ -10,6 +10,7 @@ jQuery.support = (function() {
 		eventName,
 		i,
 		isSupported,
+		clickFn,
 		div = document.createElement("div");
 
 	// Preliminary tests
@@ -112,12 +113,13 @@ jQuery.support = (function() {
 	}
 
 	if ( !div.addEventListener && div.attachEvent && div.fireEvent ) {
-		div.attachEvent( "onclick", function() {
+		div.attachEvent( "onclick", clickFn = function() {
 			// Cloning a node shouldn't copy over any
 			// bound event handlers (IE does this)
 			support.noCloneEvent = false;
 		});
 		div.cloneNode( true ).fireEvent("onclick");
+		div.detachEvent( "onclick", clickFn );
 	}
 
 	// Check if a radio maintains its value