Bug 183918 get relative file path of linkage library
model/org.eclipse.birt.report.model.tests/test/org/eclipse/birt/report/model/library/DesignLoadLibraryTest.java
* <li>a table with dataset in library is extended triple times.
	 * <li>a table with dataset in library is extended two times.
	 * </ul>
	 * 
	 * @throws Exception
	 */
	public void testMultiExtendedElements( ) throws Exception
	{
		openDesign( "DesignWithOneCompositeLibrary.xml" ); 
		TableHandle table = (TableHandle) designHandle.findElement( "table3" ); 
		assertEquals( "CompositeLib.myTable", table 
				.getProperty( IDesignElementModel.EXTENDS_PROP ) );
		assertNotNull( table.getDataSet( ) );
		assertEquals( "Lib1.dataSet1", table 
				.getStringProperty( IReportItemModel.DATA_SET_PROP ) );
		DataSetHandle dataSet = designHandle.findDataSet( table
				.getStringProperty( IReportItemModel.DATA_SET_PROP ) );
		assertNotNull( dataSet );
		dataSet = designHandle.findDataSet( "CompositeLib.dataSet1" ); 
		assertNotNull( dataSet );
		table = (TableHandle) designHandle.findElement( "table4" ); 
		assertEquals( "CompositeLib.dataSet1", table 
				.getStringProperty( IReportItemModel.DATA_SET_PROP ) );
		dataSet = table.getDataSet( );
		assertEquals( "Lib2.dataSet1", dataSet 
				.getProperty( IDesignElementModel.EXTENDS_PROP ) );
	}
	/**
	 * Test get externalized message.
	 *