ENH: sound from a file sets its status to finished when done

- merely sets .status (by calling _onEOS) after its duration has elapsed
- seems like this behavior was intended with the _onEOS function
- doing so makes the intuitive thing happen in Builder sound components:
  blank duration = play for length of the file
- can disable with mysound.play(autoStop=False) ==> revert to old behavior
- may need more work for two of the same component in succession (seems ok now)