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/api/ListingHandle.java
*/
	public SlotHandle getDetail( )
	{
		return getSlot( IListingElementModel.DETAIL_SLOT );
	}
	/**
	 * Returns the group slot. The group slot represents the grouping levels
	 * within the report. Groups appear with the most general first, the most
	 * detailed last.
	 * 
	 * @return a handle to the group slot
	 */
	public SlotHandle getGroups( )
	{
		return getSlot( IListingElementModel.GROUP_SLOT );
	}
	/**
	 * Returns the iterator for sort list defined on a table or list. The
	 * element in the iterator is the corresponding <code>StructureHandle</code>
	 * that deal with a <code>SortKey</code> in the list.
	 * 
	 * @return the iterator for <code>SortKey</code> structure list defined on
	 *         a table or list.
	 */
	public Iterator sortsIterator( )
	{
		PropertyHandle propHandle = getPropertyHandle( IListingElementModel.SORT_PROP );
		assert propHandle != null;
		return propHandle.iterator( );
	}