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
*            report item
		 */
		private BaseQueryDefinition prepareVisit( ReportItemDesign item )
		{
			BaseQueryDefinition tempQuery = null;
			if ( item instanceof ListingDesign )
				tempQuery = createQuery( (ListingDesign) item );
			else
				tempQuery = createQuery( item );
			if ( tempQuery != null )
			{
				pushQuery( tempQuery );
				pushExpressions( tempQuery.getRowExpressions( ) );
			}
			return tempQuery;
		}
		/**
		 * Clean up stack after visiting a report item
		 */
		private void finishVisit( BaseQueryDefinition query )
		{
			if ( query != null )
			{
				popExpressions( );
				popQuery( );
			}
		}
		/*
		 * (non-Javadoc)
		 *