onstream: event.blobURL is fixed for Firefox.

[`onstream`](http://www.rtcmulticonnection.org/docs/onstream/):
"event.blobURL" for Firefox, fixed. Previously it was returning
"MediaStream" object.

```javascript
connection.onstream = function(e)
{
    // e.blobURL -- now it is always blob:URI
};
```

`connection.DetectRTC.hasSpeakers` added. It works only on Chrome
Canary, though.