Bug 305739 [viewers] #expandToLevel(Object, level) retrieves all children when virtual
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
Item item = items[i];
			Object data = item.getData();
			TreePath childPath = data == null ? null : currentPath
					.createChildPath(data);
			if (data != null && childPath != null) {
				
				
				boolean expanded = expandedTreePaths.remove(childPath) != null;
				if (expanded != getExpanded(item)) {
					if (expanded) {
						createChildren(item);
					}
					setExpanded(item, expanded);
				}
			}
			internalSetExpandedTreePaths(expandedTreePaths, item, childPath);
		}
	}
	/**
	 * Return whether the tree node representing the given element or path can
	 * be expanded. Clients should query expandability by path if the viewer's
	 * content provider is an {@link ITreePathContentProvider}.
	 * <p>
	 * The default implementation of this framework method calls
	 * <code>hasChildren</code> on this viewer's content provider. It may be
	 * overridden if necessary.
	 * </p>
	 *
	 * @param elementOrTreePath
	 *            the element or path