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/elements/interfaces/IListingElementModel.java
public static final int HEADER_SLOT = 0;
	/**
	 * Identifies the slot that contains the list of groups.
	 */
	public static final int GROUP_SLOT = 1;
	/**
	 * Identifies the detail slot. The detail section prints for each row from
	 * the data set.
	 */
	public static final int DETAIL_SLOT = 2;
	/**
	 * Identifies the footer slot. The footer slot prints at the end of the
	 * listing and often contains totals.
	 */
	public static final int FOOTER_SLOT = 3;
	/**
	 * Name of the Sort property.
	 */
	public static final String SORT_PROP = "sort"; 
	/**
	 * Name of the filter property. This defines the filter criteria to match
	 * the rows to appear.
	 */
	public static final String FILTER_PROP = "filter"; 
	
	/**
	 * Name of the pageBreakInterval property. 
	 */
	public static final String PAGE_BREAK_INTERVAL_PROP = "pageBreakInterval"; 
	/**