Bug 136270 Group's data binding column can only be used by the group itself
If you add some data binding columns to a group, these columns can only be used by this group itself. It should has a way to make the child can use the parent group's data binding column.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
* 
	 * @param parent
	 * @return slot id, -1 if not found
	 */
	public static int getDefaultSlotID( Object parent )
	{
		int slotID = -1;
		if ( parent instanceof GraphicMasterPageHandle )
		{
			slotID = GraphicMasterPageHandle.CONTENT_SLOT;
		}
		else if ( parent instanceof ParameterGroupHandle )
		{
			slotID = ParameterGroupHandle.PARAMETERS_SLOT;
		}
		else if ( parent instanceof ReportDesignHandle )
		{
			slotID = ReportDesignHandle.BODY_SLOT;
		}
		else if ( parent instanceof LibraryHandle )
		{
			slotID = ModuleHandle.COMPONENT_SLOT;
		}
		else if ( parent instanceof CellHandle )
		{
			slotID = CellHandle.CONTENT_SLOT;
		}
		else if ( parent instanceof RowHandle )
		{
			slotID = RowHandle.CONTENT_SLOT;