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 dataSetList;
	}
	/**
	 * Get definition of model property.
	 * 
	 * @param elementName
	 * @param propertyName
	 */
	public static IElementPropertyDefn getPropertyDefn( String elementName,
			String propertyName )
	{
		IElementDefn elementDefn = DesignEngine.getMetaDataDictionary( )
				.getElement( elementName );
		if ( elementDefn != null )
		{
			return elementDefn.getProperty( propertyName );
		}
		return null;
	}
	/**
	 * Gets the proper expression for the given model
	 * 
	 * @param model
	 *            the given model
	 * @return Returns the proper expression for the given model, or null if no
	 *         proper one exists
	 */
	public static String getExpression( Object model )
	{
		if ( model instanceof ParameterHandle )