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
*            the XML attribute name
	 * @param propName
	 *            the name of the property to write
	 */
	protected void attribute( DesignElement obj, String attr, String propName )
	{
		ElementPropertyDefn prop = obj.getPropertyDefn( propName );
		assert prop != null;
		Object value = obj.getLocalProperty( getModule( ), prop );
		if ( value == null )
			return;
		String xml = prop.getXmlValue( getModule( ), value );
		if ( xml == null )
			return;
		writer.attribute( attr, xml );
	}
	/**
	 * Writes one property entry of an element.
	 * 
	 * @param obj
	 *            the design element
	 * @param propName
	 *            the property name
	 */
	protected void property( DesignElement obj, String propName )
	{
		writeProperty( obj, null, propName, false );
	}
	/**
	 * Writes one property entry of an structure.