Bug 122854 There is redundant columns in "available columns" list in "export data" dialog.
Description: There is redundant columns in "available columns" list in "export data" dialog. Steps to reproduce: 1. Preview attached design in web viewer. 2. Select the table and click on "export" button. 3. There is a "detail" column name in "available columns" list which is not data set column.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/ReportQueryBuilder.java
{
			BaseQueryDefinition query = prepareVisit( label );
			handleReportItemExpressions( label );
			handleAction( label.getAction( ) );
			finishVisit( query );
			return value;
		}
		/*
		 * (non-Javadoc)
		 * 
		 * @see org.eclipse.birt.report.engine.ir.IReportItemVisitor#visitExtendedItem(org.eclipse.birt.report.engine.ir.ExtendedItemDesign)
		 */
		public Object visitExtendedItem( ExtendedItemDesign item, Object value )
		{
			
			ExtendedItemHandle handle = (ExtendedItemHandle) item.getHandle( );
			String tagName = handle.getExtensionName( );
			
			
			
			IReportItemQuery itemQuery = ExtensionManager.getInstance( )
					.createQueryItem( tagName );
			IBaseQueryDefinition[] queries = null;
			IBaseQueryDefinition parentQuery = getParentQuery( );
			IBaseTransform parentTrans = getTransform( );
			if ( itemQuery != null )
			{
				try
				{
					itemQuery.setModelObject( handle );