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
return false;
				break;
			}
			case CompiledExpression.TYPE_CONSTANT_EXPR :
			case CompiledExpression.TYPE_INVALID_EXPR :
			{
				break;
			}
		}
		return true;
	}
	
	/**
	 * 
	 * @param aggName
	 * @return
	 */
	private static boolean isTopBottomN( String aggName )
	{
		if ( BuiltInAggregationFactory.TOTAL_BOTTOM_N_FUNC.equals( aggName )
				|| BuiltInAggregationFactory.TOTAL_BOTTOM_PERCENT_FUNC.equals( aggName )
				|| BuiltInAggregationFactory.TOTAL_TOP_N_FUNC.equals( aggName )
				|| BuiltInAggregationFactory.TOTAL_TOP_PERCENT_FUNC.equals( aggName ) )
			return true;
		else
			return false;
	}
	
	/**
	 *