Bug 200471 Add "need not sort for grouping" option in report item
Currently when Data engine proceeds groups, it always sorts the result set according to given group key.However that should not be necessary when the raw data is already sorted. So we'd like to add new options so that user can indicate whether should we sort the data before grouping. In model, we should allow user to set a "need not do sort for grouping" option to all the report element that can be grouped(table, list,etc.)
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/writer/ModuleWriter.java
* 
	 * @param obj
	 *            the structure to write
	 * @param memberName
	 *            the name of the structure list property to write
	 */
	private void writeStructureList( IStructure obj, String memberName )
	{
		PropertyDefn prop = (PropertyDefn) obj.getDefn( )
				.getMember( memberName );
		assert prop != null;
		assert prop.getTypeCode( ) == IPropertyType.STRUCT_TYPE
				&& prop.isList( );
		assert obj instanceof Structure;
		List list = (List) ( (Structure) obj ).getLocalProperty( getModule( ),
				prop );
		if ( list == null || list.size( ) == 0 )
			return;
		writer.startElement( DesignSchemaConstants.LIST_PROPERTY_TAG );
		writer.attribute( DesignSchemaConstants.NAME_ATTRIB, memberName );
		Iterator iter = list.iterator( );
		while ( iter.hasNext( ) )
		{
			IStructure struct = (IStructure) iter.next( );
			writer.startElement( DesignSchemaConstants.STRUCTURE_TAG );
			Iterator memberIter = prop.getStructDefn( ).propertiesIterator( );
			while ( memberIter.hasNext( ) )
			{
				PropertyDefn memberDefn = (PropertyDefn) memberIter.next( );