Bug 121498 When datasource/dataset deleted, the datasource/dataset property binding element haven't been deleted
When deleted the datasource/dataset, the datasource/dataset property binding element haven't been deleted. Expected result: This operation must be a transaction.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/Module.java
DesignElement client = ref.element;
			ElementRefValue value = (ElementRefValue) client.getLocalProperty(
					this, ref.propName );
			value.unresolved( value.getName( ) );
			referred.dropClient( client );
			if ( IStyledElementModel.STYLE_PROP.equalsIgnoreCase( ref.propName ) )
				client.broadcast( new StyleEvent( client ) );
			else
				client.resolveElementReference( this, client
						.getPropertyDefn( ref.propName ) );
		}
	}
	/**
	 * Returns whether this module is read-only.
	 * 
	 * @return true, if this module is read-only. Otherwise, return false.
	 */
	public boolean isReadOnly( )
	{
		return activityStack instanceof ReadOnlyActivityStack;
	}
	/**
	 * Adds one attribute listener. The duplicate listener will not be added.
	 * 
	 * @param listener
	 *            the attribute listener to add
	 */
	public void addAttributeListener( IAttributeListener listener )
	{
		if ( attributeListeners == null )