* tree.c: Added an initial version of xmlDOMWrapCloneNode() to
  the API. It will be used to reflect DOM's Node.cloneNode and
  Document.importNode methods.
  The pros: 1) non-recursive, 2) optimized ns-lookup
  (mostly pointer comparison), 3) user defined ns-lookup,
  4) save ns-processing. The function is in an unfinished
  and experimental state and should be only used to test it.