Bug 176107 row.__rownum cannot be directly used as group key
Create a table that bind it to a data set. Insert a group. For the Group On field, click on the "..." button to edit the expression, and select from "Availble Column Bindings" | "Table" | "RowNum". This creates a Group On Expression "row.__rownum". The resulting report design cannot be run. It produces error: Column binding "row.__rownum" does not exist. To workaround this, one must create another binding on the table and set its expression to "row.__rownum", then use the new binding as group key. This should not have been necessary. The "__rownum" binding should be implicitly available in all contexts that have a data set. E.g., it should be usable directly as group key, sort key, and in conditional format expressions, etc. Attached is a sample report that produces the error.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/expression/ExpressionCompilerUtil.java
{
			Context.exit( );
		}
	}
	/**
	 * 
	 * @param expr
	 */
	private static boolean flattenExpression( CompiledExpression expr,
			ExprManager exprManager )
	{
		int type = expr.getType( );
		switch ( type )
		{
			case CompiledExpression.TYPE_COMPLEX_EXPR :
			{
				Iterator col = ( (ComplexExpression) expr ).getSubExpressions( )
						.iterator( );
				while ( col.hasNext( ) )
				{
					if ( !flattenExpression( (CompiledExpression) col.next( ),
							exprManager ) )
						return false;
				}
				break;
			}
			case CompiledExpression.TYPE_DIRECT_COL_REF :
			{
				String columnName = ( (ColumnReferenceExpression) expr ).getColumnName( );
				if ( ROWNUM.equals(columnName))