Propagating the event to the MessagePort is transparent to the user
Support for Internet Explorer 8 and `attachEvent`
Fix a race condition and teardown with IE8
Compute iframe url
Restore window.postMessage between tests
Web worker communication works
Fix a bug when a port is sent with queued messages,

When we have multiple listeners that decode the event, each of them
should not copy the event on the port or we get duplicate events.
Make test suite compatible for browsers that don't support web workers
Merge pull request #4 from Cyril-sf/addEventListener

Internet Explorer 8 support