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
assert resultSetName != null;
		assert executionContext.getDataEngine() != null;
		
		if( isMetaDataPrepared == false )
		{
			prepareMetaData( );
		}
		DataEngine dataEngine = executionContext.getDataEngine().getDataEngine();
		try
		{
			IQueryDefinition query = (IQueryDefinition)mapResultSetToQuery.get( resultSetName );
			assert query != null;
			validateSelectedColumns( query );
			
			IQueryResults queryResults = dataEngine.getQueryResults( resultSetName );
			assert queryResults.getResultIterator() != null;
			 
			currentResult = new ExtractionResults( queryResults.getResultIterator() 
					, selectedColumns, getScriptExpressions( query.getRowExpressions()) );
			return currentResult;
		}
		catch ( BirtException e )
		{
			e.printStackTrace( );
		}
		return null;
	}
	
	/*
	 * data export by report item instance