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/api/impl/DataExtractionTask.java
public DataExtractionTask( ReportEngine engine, IReportRunnable runnable,
			ReportDocumentReader reader ) throws EngineException
	{
		super( engine, runnable );
		
		
		this.reportDocReader = reader;
		executionContext.setReportDocument( reportDocReader );
		executionContext.setFactoryMode( false );
		executionContext.setPresentationMode( true );
		report = new ReportParser( ).parse( ( (ReportRunnable) runnable )
				.getReport( ) );
		
		executionContext.setReport( report );
		setParameterValues( reportDocReader.getParameterValues( ) );
		
		
		
		IDataEngine dataEngine = executionContext.getDataEngine();
		dataEngine.prepare( report, appContext );
	}
	
	/*
	 * prepare the meta data of DataExtractionTask.
	 */
	private void prepareMetaData( ) throws EngineException
	{
		ReportQueryBuilder queryBuilder = new ReportQueryBuilder( );
		
		queryBuilder.build( report, executionContext );