add matchTarget to event forwarded by on()

See https://bugs.dojotoolkit.org/ticket/18355
There's no reason to use an array with a timeout to check test results. The following should work:

```js
var dfd = new doh.Deferred();
on(div, "click", dfd.getTestCallback(lang.hitch(that, function (e) {
    t.is(this === that);
})));
```