handle is null error on IE6 after ComboBox_mouse test and page unload

[bill]

Steps to reproduce:

1. start IE6
2. run dijit/tests/form/robot/_autoComplete_mouse.html?testWidget=dijit.form.ComboBox? (and wait for it to finish)
3. shutdown IE, or refresh the page, or try to navigate to a different page.

It gets an error about "handle is null" from the code:

ready(function(){
	var handle = singleton.registerWin(win.doc.parentWindow || win.doc.defaultView);
	if(has("ie")){
		unload.addOnWindowUnload(function(){
			handle.remove();
			handle = null;
		})
	}
});

Obviously IE needs to be setup for script debugging to see this.

Doesn't happen merely by loading test_ComboBox.html.

[bill]

See #14157. Either the dojo/on needs to be redesigned or dojo/robotx.js needs to be changed not to connect to a node in another frame.

[bill]

This was actually started working in [27059], and there was also a work-around added in [27137], although that's can be removed now that #14157 is fixed. Anyway, I'm going to close this ticket.