get_events
Description:
Returns the event mask (see EventMask) for the widget.
These are the events that the widget will receive.
Note: Internally, the widget event mask will be the logical OR of the event mask set through set_events or add_events, and the event mask necessary to cater for every EventController created for the widget.
Parameters:
| this | 
           a Widget  | 
      
Returns:
| 
           event mask for this  |