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.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
for (MWindow dw : win.getWindows()) {
				if (isInContainer(dw, element))
					return true;
			}
		}
		if (container instanceof MPerspective) {
			MPerspective persp = (MPerspective) container;
			for (MWindow dw : persp.getWindows()) {
				if (isInContainer(dw, element))
					return true;
			}
		}
		return false;
	}
	MPlaceholder getLocalPlaceholder(MUIElement part) {
		return modelService.findPlaceholderFor(getWindow(), part);
	}
	public void switchPerspective(MPerspective perspective) {
		Assert.isNotNull(perspective);
		MWindow window = getWindow();
		if (window != null && isInContainer(window, perspective)) {
			perspective.getParent().setSelectedElement(perspective);
			List<MPart> newPerspectiveParts = modelService.findElements(perspective, null,
					MPart.class, null);
			
			if (newPerspectiveParts.contains(activePart)
					&& partActivationHistory.isValid(perspective, activePart)) {
				MPart target = activePart;
				IEclipseContext activeChild = activePart.getContext().getParent().getActiveChild();
				if (activeChild != null) {