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
initialize(applicationContext, application);
		
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		partService.activate(partA);
		Object o = applicationContext.get(IServiceConstants.ACTIVE_PART);
		assertEquals(partA, o);
		partService.activate(partB);
		o = applicationContext.get(IServiceConstants.ACTIVE_PART);
		assertEquals(partB, o);
	}
	private MApplication createApplication(String partId) {
		return createApplication(new String[] { partId });
	}
	private MApplication createApplication(String... partIds) {
		return createApplication(new String[][] { partIds });
	}
	private MApplication createApplication(String[]... partIds) {
		return createApplication(partIds.length, partIds);
	}
	private MApplication createApplication(int windows, String[][] partIds) {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		for (int i = 0; i < windows; i++) {
			MWindow window = MApplicationFactory.eINSTANCE.createWindow();
			application.getChildren().add(window);
			MPartStack partStack = MApplicationFactory.eINSTANCE
					.createPartStack();