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
*/
	protected void writeContents( DesignElement obj, String propName )
	{
		writeContents( new ContainerContext( obj, propName ),
				DesignSchemaConstants.PROPERTY_TAG );
	}
	/**
	 * Writes the contents of a slot. The order is not the order in the slot
	 * while we first write the ancestor and then the derived ones. The contents
	 * are enclosed in an optional list tag.
	 * 
	 * @param obj
	 *            the container element
	 * @param slot
	 *            the slot to write
	 * @param tag
	 *            the optional list tag that encloses the list of contents
	 */
	protected void writeArrangedContents( DesignElement obj, int slot,
			String tag )
	{
		List list = obj.getSlot( slot ).getContents( );
		if ( list.isEmpty( ) )
			return;
		LinkedList newList = new LinkedList( );
		Iterator iter = list.iterator( );
		while ( iter.hasNext( ) )
		{
			DesignElement element = (DesignElement) iter.next( );
			DesignElement parent = element.getExtendsElement( );