function collectSelectableNodes(aNodes) {
			jQuery.each(aNodes, function(i, oNode) {
				if (oNode.getSelectable()) {
					aSelectableNodes.push(oNode);
				}
				if (oNode.getExpanded()) {
					collectSelectableNodes(oNode._getNodes());
				}
			});
		}
Rerendering handling. Remembers the scroll position of the selected node.
@private