Bug 307747 EPartService doesn't render new parts
1. Have a part in a stack, it is the selected part. 2. Show another part in that stack using PartState.CREATE or PartState.VISIBLE. 3. The part should've been rendered. It is not.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
partDescriptor.setId("partId");
		application.getDescriptors().add(partDescriptor);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		assertNull(partService.createPart("partId2"));
	}
	public void testShowPart_Id_ACTIVATE() {
		MApplication application = createApplication(1, new String[1][0]);
		MWindow window = application.getChildren().get(0);
		MPartDescriptor partDescriptor = MApplicationFactory.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setId("partId");
		application.getDescriptors().add(partDescriptor);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart part = partService.showPart("partId", PartState.ACTIVATE);
		assertNotNull(part);
		assertEquals("partId", part.getId());
		assertEquals(part, partService.getActivePart());
		assertTrue("Shown part should be visible", part.isVisible());
	}
	public void testShowPart_Id_ACTIVATE_DefinedCategoryStackNotExists() {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		MWindow window = MApplicationFactory.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPartDescriptor partDescriptor = MApplicationFactory.eINSTANCE