S-GEO: watchPosition() Reimplemented
    
    navigator.geolocation.watchPosition intended use concerns tracking user position changes.
    JSR will provide four modes of operaion:
    * GEO OFF: navigator.geolocation is undefined. FIXME implement
    * user supplied position: Always return the same data, the same as getCurrentPosition()
    * current position approximation: Always return the same data, the same as getCurrentPosition()
    * accurate data: Return exact position but fake timestamp FIXME implement
    
    The current implementation copes with option 2 and 3, i.e. callbacks the
    same results as getCurrentPosition.