Bug 129144 Support suppressDuplicates property on table row in report engine
See 129143 for detail. This only needs to be supported for data item in a detail row of a table.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/executor/ListingElementExecutor.java
/**
	 * emitter used to output the content
	 */
	protected IContentEmitter outputEmitter;
	/**
	 * @param context
	 *            execution context
	 * @param visitor
	 *            the visitor object that drives exection
	 */
	protected ListingElementExecutor( ExecutionContext context,
			IReportItemVisitor visitor )
	{
		super( context, visitor );
	}
	/**
	 * access the query and create the contents. the execution process is:
	 * <li> the cursor is at the begin of result set.
	 * <li> call listing's onStart event
	 * <li> create the header
	 * <li> for each row:
	 * <ul>
	 * <li> call onRow event.
	 * <li> if the row start some groups, create the group header for that
	 * group.
	 * <li> create the detail row.
	 * <li> if the row end some groups, create the group footer for that group.
	 * </ul>
	 * <li> create the footer.
	 * <li> call the onFinish event.