Bug 337002 EPartService leaks previously active part
A reference is kept to the previously active part. This is unnecessary. We only need it to fire events. After the deactivation events have been fired, we should no longer need to keep it lying around.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
* Test to ensure that we can handle the showing of a part that's under a
	 * container with a selected element that's invalid.
	 */
	private void testShowPart_Bug328078(PartState partState) {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPartStack partStack = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(partStack);
		window.setSelectedElement(partStack);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partA);
		partStack.setSelectedElement(partA);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partStack.getChildren().add(partB);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		
		partStack.getChildren().remove(partA);
		
		partService.showPart(partB, partState);
		assertEquals(partB, partStack.getSelectedElement());
	}
	public void testShowPart_Bug328078_CREATE() {
		testShowPart_Bug328078(PartState.CREATE);
	}