SLING-3639 partial fix : more node type changes are now possible - but round-trippping from nt:unstructured->sling:Folder back to nt:unstructured doesn't result in original structure. More refinements needed - but probably 1.0.2

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1602433 13f79535-47bb-0310-9956-ffa450edef68