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
* A helper function for removing a query from query stack
		 */
		protected void popQuery( )
		{
			assert !queryStack.isEmpty( );
			queryStack.removeLast( );
		}
		/**
		 * add expression to the expression collection on top of the expressions
		 * stack
		 * 
		 * @param expr
		 *            expression to be added
		 */
		protected void addExpression( IBaseExpression expr )
		{
			
			
			if ( expr != null && expressions != null )
				expressions.add( expr );
		}
		/**
		 * @return topmost element on query stack
		 */
		protected IBaseTransform getTransform( )
		{
			if ( queryStack.isEmpty( ) )
				return null;
			return (IBaseTransform) queryStack.getLast( );
		}