Return !defaultPrevented from Target#dispatchEvent{Named}

to align with the spec http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventTarget-dispatchEvent
Return !defaultPrevented from AbstractControl#dispatchActionEvent

to align with the spec http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventTarget-dispatchEvent

And add tests.
Merge pull request #1279 from Stuk/dispatchEvent

return defaultPrevented from dispatchEvent