Refresh containment for helper during the dragging

Refresh containment for helper during the dragging

Hi!

I have document as the containment for helper. During the dragging document may be increased, on the specific event.

How I can refresh cached containment boundaries?

Now I have to use private methods like this:

```
//somewhere inside my event handler
$.ui.ddmanager.current.document = $(document);
$.ui.ddmanager.current._setContainment();
```

Thanks!