Bug 313382 No 'X' close buttons on views
The renderer is currently ignoring the 'closeable' feature for MParts if it's actually represented by a placeholder (i.e. 3.x views).
bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/workbench/ui/renderers/swt/StackRenderer.java
Composite parentComposite = (Composite) parent;
		
		int styleModifier = 0; 
		final CTabFolder ctf = new CTabFolder(parentComposite, SWT.BORDER
				| styleModifier);
		bindWidget(element, ctf); 
		return ctf;
	}
	protected void createTab(MElementContainer<MUIElement> stack,
			MUIElement element) {
		MPart part = null;
		if (element instanceof MPart)
			part = (MPart) element;
		else if (element instanceof MPlaceholder)
			part = (MPart) ((MPlaceholder) element).getRef();
		CTabFolder ctf = (CTabFolder) stack.getWidget();
		CTabItem cti = findItemForPart(element, stack);
		if (cti != null) {
			if (element.getWidget() != null)
				cti.setControl((Control) element.getWidget());
			return;
		}
		int createFlags = SWT.NONE;
		if (element instanceof MPart && ((MPart) element).isCloseable()) {
			createFlags |= SWT.CLOSE;
		}
		
		int index = calcIndexFor(stack, element);
		cti = new CTabItem(ctf, createFlags, index);
		cti.setData(OWNING_ME, element);