Remember to call EventEmitter superclass constructor.

Without this call, `this.domain`, `this._events` and `this._maxListeners`
will not be properly initialized.
Remember to call more superclass constructors.

Notice that we were coping with this oversight by duplicating code in
subclass constructors.
Merge pull request #7 from benjamn/call-EventEmitter-constructor

Remember to call EventEmitter superclass constructor