Bug 159918 [Viewers] TreeViewer.setChildCount(...) should preserve selection
Since changing the child count of an element in a tree can effectively remove children, the #setChildCount(...) method should preserve selection. This way if a selected item is disposed, the selection change will fire with the new <empty selection>.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
private static final String VIRTUAL_DISPOSE_KEY = Policy.JFACE
			+ ".DISPOSE_LISTENER"; 
	/**
	 * Internal tree viewer implementation.
	 */
	private TreeEditorImpl treeViewerImpl;
	/**
	 * This viewer's control.
	 */
	private Tree tree;
	/**
	 * This viewer's tree editor.
	 */
	private TreeEditor treeEditor;
	/**