Bug 326087 StackRenderer arbitrarily changes selected element when MPartStack is being unrendered
1. Open two files. 2. Activate the editor in the back. 3. Restart 4. The file in the wrong is active now. :O
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		descriptor.setElementId("part");
		descriptor.setCategory("aStack");
		application.getDescriptors().add(descriptor);
		MPartDescriptor descriptor2 = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		descriptor2
				.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		descriptor2.setElementId("part2");
		descriptor2.setCategory("aStack");
		application.getDescriptors().add(descriptor2);
		
		
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		MPartSashContainer partSashContainer = BasicFactoryImpl.eINSTANCE
				.createPartSashContainer();
		MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
		
		stack.setElementId("aStack");
		partSashContainer.getChildren().add(stack);
		window.getChildren().add(partSashContainer);
		application.getChildren().add(window);
		
		MWindow window2 = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window2);
		wb = new E4Workbench(application, appContext);
		wb.createAndRunUI(window);
		IPresentationEngine engine = appContext.get(IPresentationEngine.class);
		engine.createGui(window2);