Bug 184563 Need clearAggregateOns() api on ComputedColumnHandle
Since current aggregateOn in ComputedColumn could be a list, we need a convenient method to clear all the values in one call.
model/org.eclipse.birt.report.model.tests/test/org/eclipse/birt/report/model/api/ComputedColumnHandleTest.java
* To test add/remove methods on aggregateOn and argument lists.
	 * 
	 * @throws Exception
	 */
	public void testSimpleListProperties( ) throws Exception
	{
		createDesign( );
		DataItemHandle data = designHandle.getElementFactory( ).newDataItem(
				"data1" ); 
		designHandle.getBody( ).add( data );
		ComputedColumn column = StructureFactory.createComputedColumn( );
		column.setName( "column 1" ); 
		column.setExpression( "expression 1" ); 
		ComputedColumnHandle columnHandle = data.addColumnBinding( column,
				false );
		columnHandle.addArgument( "argument 1" ); 
		List arguments = columnHandle.getArgumentList( );
		assertEquals( 1, arguments.size( ) );
		columnHandle.removeArgument( "argument 1" ); 
		arguments = columnHandle.getArgumentList( );
		assertEquals( 0, arguments.size( ) );
		columnHandle.addAggregateOn( "group 1" ); 
		List aggregates = columnHandle.getAggregateOnList( );
		assertEquals( 1, aggregates.size( ) );
		columnHandle.removeAggregateOn( "group 1" ); 
		aggregates = columnHandle.getAggregateOnList( );
		assertEquals( 0, aggregates.size( ) );
	}
}