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/ir/Report.java
* @param id the component id
	 * @return the report item instance
	 */
	public ReportElementDesign getReportItemByID( long id )
	{
		assert mapReportItemIDtoInstance != null;
		return (ReportElementDesign) mapReportItemIDtoInstance.get( new Long( id ) );
	}
	/**
	 * return the named expression defined on the report
	 * @return
	 */
	public Map getNamedExpressions( )
	{
		if( namedExpressions == null )
			namedExpressions = new HashMap( );
		
		return namedExpressions;
	}
	/**
	 * set the report's page setup
	 * 
	 * @param pageSetup
	 *            page setup
	 */
	public void setPageSetup( PageSetupDesign pageSetup )
	{
		this.pageSetup = pageSetup;
	}
	/**