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
*            the handle of the element
	 * @return the list of all visible column bindings.The list order is from
	 *         the top to the given element
	 */
	public static List getVisiableColumnBindingsList(
			DesignElementHandle handle, boolean includeSelf )
	{
		List bindingList = new ArrayList( );
		if ( includeSelf )
		{
			Iterator iterator = getBindingColumnIterator( handle );
			while ( iterator.hasNext( ) )
			{
				bindingList.add( iterator.next( ) );
			}
		}
		ReportItemHandle holder = getBindingHolder( handle );
		if ( holder != null )
		{
			for ( DesignElementHandle elementHandle = handle.getContainer( ); elementHandle != holder.getContainer( ); elementHandle = elementHandle.getContainer( ) )
			{
				List subBindingList = new ArrayList( );
				Iterator iterator = getBindingColumnIterator( elementHandle );
				while ( iterator.hasNext( ) )
				{
					subBindingList.add( iterator.next( ) );
				}
				bindingList.addAll( 0, subBindingList );
			}
		}