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
/**
	 * Returns the iterator for filter list defined on a table or list. The
	 * element in the iterator is the corresponding <code>StructureHandle</code>
	 * that deal with a <code>FilterCond</code> in the list.
	 * 
	 * @return the iterator for <code>FilterCond</code> structure list defined
	 *         on a table or list.
	 */
	public Iterator filtersIterator( )
	{
		PropertyHandle propHandle = getPropertyHandle( IListingElementModel.FILTER_PROP );
		assert propHandle != null;
		return propHandle.iterator( );
	}
	/**
	 * Returns the page break interval value
	 * 
	 * @return the page break interval value
	 */
	public int getPageBreakInterval( )
	{
		return getIntProperty( IListingElementModel.PAGE_BREAK_INTERVAL_PROP );
	}
	/**
	 * Sets the page break interval value
	 * 
	 * @param pageBreakInterval
	 *            the page break interval
	 * @throws SemanticException
	 *             if the parameter is not a valid integer