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 ListingHandle( Module module, DesignElement element )
	{
		super( module, element );
	}
	/**
	 * Returns the header slot. The header slot represents subsections that
	 * print at the start of the listing.
	 * 
	 * @return a handle to the header slot
	 */
	public SlotHandle getHeader( )
	{
		return getSlot( IListingElementModel.HEADER_SLOT );
	}
	/**
	 * Returns the footer slot. The footer slot represents subsections that
	 * print at the end of the listing.
	 * 
	 * @return a handle to the footer slot
	 */
	public SlotHandle getFooter( )
	{
		return getSlot( IListingElementModel.FOOTER_SLOT );
	}
	/**
	 * Returns the detail slot. The detail slot represents subsections that
	 * print for each row in the data set.
	 * 
	 * @return a handle to the detail slot