Bug 183918 get relative file path of linkage library
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ComplexPropertyCommand.java
* @param oldPosn
	 *            the old position of the item.
	 * @param newPosn
	 *            new position of the item. Note that the range of
	 *            <code>to</code> is from 0 to the number of strucutres in the
	 *            list.
	 * 
	 * @throws PropertyValueException
	 *             if the property is not a structure list property, or the list
	 *             value is not set.
	 * @throws IndexOutOfBoundsException
	 *             if the given from or to index is out of range
	 *             <code>(index &lt; 0 || index &gt;= list.size())</code>.
	 */
	public void moveItem( MemberRef ref, int oldPosn, int newPosn )
			throws PropertyValueException
	{
		assert ref != null;
		checkAllowedOperation( );
		PropertyDefn propDefn = ref.getPropDefn( );
		assert propDefn != null;
		checkListMemberRef( ref );
		List list = ref.getList( module, element );
		if ( list == null )
			throw new PropertyValueException( element, ref.getPropDefn( ),
					null,
					PropertyValueException.DESIGN_EXCEPTION_ITEM_NOT_FOUND );
		ActivityStack stack = getActivityStack( );
		String label = ModelMessages
				.getMessage( MessageConstants.MOVE_ITEM_MESSAGE );