Bug 342849 [UI] Allow dragging stacks
We have yet to implement the ability to drag a complete stack (rather than a part) in the presentation. The first pass for this will allow dragging a stack but only to locate the stack itself in a different part of the presentation. While it's possible to also allow dragging a stack to 'merge' it with the parts in some other stack this is of less use and introduces a possibly confusing scenario: If I have a stack with "A", "B" and "C" in it but only "A" and "B" are currently visible then the result of the merge should be to only move "A" and "B" into the merged stack, leaving "C" in the original stack.
bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/dndaddon/SplitDropAgent.java
private Rectangle ctfBounds;
	/**
	 * @param modelService
	 *            The model service related to this agent
	 * 
	 */
	public SplitDropAgent(DnDManager manager) {
		super(manager);
	}
	@Override
	public boolean canDrop(MUIElement dragElement, DnDInfo info) {
		if (!(dragElement instanceof MStackElement))
			return false;
		if (!(info.curElement instanceof MStackElement))
			return false;
		
		MUIElement parent = info.curElement.getParent();
		if (info.curElement instanceof MPart && info.curElement.getCurSharedRef() != null)
			parent = info.curElement.getCurSharedRef().getParent();
		if (!(parent instanceof MPartStack) || !(parent.getWidget() instanceof CTabFolder))
			return false;
		dropStack = (MPartStack) parent;
		weight = dropStack.getContainerData();
		dropCTF = (CTabFolder) parent.getWidget();
		return true;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.e4.ui.workbench.addons.dndaddon.DropAgent#dragEnter(org.eclipse.e4.ui.model.