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
return bindingList;
	}
	/**
	 * Returns the element handle which can save binding columns the given
	 * element
	 * 
	 * @param handle
	 *            the handle of the element which needs binding columns
	 * @return the holder for the element,or itself if no holder available
	 */
	public static ReportItemHandle getBindingHolder( DesignElementHandle handle )
	{
		if ( handle instanceof ReportElementHandle )
		{
			if ( handle instanceof ListingHandle
					|| handle instanceof GridHandle )
			{
				return (ReportItemHandle) handle;
			}
			ReportItemHandle result = getBindingHolder( handle.getContainer( ) );
			if ( result == null && handle instanceof ReportItemHandle )
			{
				result = (ReportItemHandle) handle;
			}
			return result;
		}
		return null;
	}
	/**
	 * Add a binding column on the given element