Bug 327044 EPartService's hidePart(*) should unset the part's parent element if the part is the selected element
It is not valid to have a selected element that's TBR flag is 'false'.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
partStackB.setSelectedElement(partFrontB);
		getEngine().createGui(windowA);
		getEngine().createGui(windowB);
		EPartService partServiceA = (EPartService) partFrontA.getContext().get(
				EPartService.class.getName());
		EPartService partServiceB = (EPartService) partFrontB.getContext().get(
				EPartService.class.getName());
		partServiceA.bringToTop(partBackB);
		assertEquals(partStackA.getSelectedElement(), partFrontA);
		assertEquals(partStackB.getSelectedElement(), partFrontB);
		partServiceB.bringToTop(partBackA);
		assertEquals(partStackA.getSelectedElement(), partFrontA);
		assertEquals(partStackB.getSelectedElement(), partFrontB);
		partServiceA.bringToTop(partBackA);
		assertEquals(partStackA.getSelectedElement(), partBackA);
		assertEquals(partStackB.getSelectedElement(), partFrontB);
		partServiceB.bringToTop(partBackB);
		assertEquals(partStackA.getSelectedElement(), partBackA);
		assertEquals(partStackB.getSelectedElement(), partBackB);
	}
	public void testBringToTop_ActivationChanges() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPartStack partStackA = BasicFactoryImpl.eINSTANCE.createPartStack();
		MPart partFrontA = BasicFactoryImpl.eINSTANCE.createPart();
		MPart partBackA = BasicFactoryImpl.eINSTANCE.createPart();
		partStackA.getChildren().add(partFrontA);
		partStackA.getChildren().add(partBackA);