component events should mask event propagation.

[mhevery]

@Component({
  selector: 'my-component'
  events: ['change']
})
@View({
  template: '<input (change)="...">'
})
class MyComponent {
} 

The above code creates an issue. It conflates the change event from the MyComponent with the bubbling change event from the <input>.

The correct behavior is that the change event which is part of the components should filter out the DOM change events. Otherwise

<my-component (change)="doSomething($event)">

will sometimes get the $event from the MyComponent and sometimes from the input event.