Dragging operation with legacy Movable/Movable2 objects

[zglueck]

Modifications in v2.1.0 to the BasicDragger and dragging mechanisms are creating issues with v2.0.0 objects implementing the Movable or Movable2 interface and not the new Draggable interface. The BasicDragger in v2.1.0 falls back to a legacy operation mode when the drag object does not implement the Draggable interface to maintain backwards compatibility.

On a DRAG_END event, the dragging state is not being set to false and the event is not consumed.

See #83 for a similar issue pertaining to legacy handling of the DRAG_END event.