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
* @see org.eclipse.birt.report.engine.ir.IReportItemVisitor#visitDataItem(org.eclipse.birt.report.engine.ir.DataItemDesign)
		 */
		public Object visitDataItem( DataItemDesign data, Object value )
		{
			BaseQueryDefinition query = prepareVisit( data );
			handleReportItemExpressions( data );
			handleAction( data.getAction( ) );
			addExpression( data.getValue( ) );
			finishVisit( query );
			return value;
		}
		/**
		 * handle expressions common to all report items
		 * 
		 * @param item
		 *            a report item
		 */
		protected void handleReportItemExpressions( ReportItemDesign item )
		{
			if ( item.getVisibility( ) != null )
			{
				for ( int i = 0; i < item.getVisibility( ).count( ); i++ )
				{
					addExpression( item.getVisibility( ).getRule( i )
							.getExpression( ) );
				}
			}
			addExpression( item.getTOC( ) );
			addExpression( item.getBookmark( ) );
			addExpression( item.getOnCreate( ) );