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
public void testShowPart_Part_ExistingInNonstandardCategory() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
		stack.setElementId("categoryId2");
		window.getChildren().add(stack);
		window.setSelectedElement(stack);
		MPart part = BasicFactoryImpl.eINSTANCE.createPart();
		part.setElementId("partId");
		stack.getChildren().add(part);
		stack.setSelectedElement(part);
		MPartDescriptor descriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		descriptor.setAllowMultiple(true);
		descriptor.setElementId("partId");
		descriptor.setCategory("categoryId");
		application.getDescriptors().add(descriptor);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart shownPart = partService.showPart("partId", PartState.ACTIVATE);
		assertEquals(part, shownPart);
		assertEquals(stack, part.getParent());
	}
	public void testShowPart_Bug318931() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE