Observe Events on forceHasSwapped

Should calling `forceHasSwapped` forcibly trigger a swap event for observing reference cursors?

For example:

``` javascript
const ref = structure.reference(['data']);
ref.observe('swap', () => {
  //should this be called?
});

const old = structure.current;
structure.forceHasSwapped(structure.undo(1), old);
```

Currently it does not appear as though it is getting called.
