give minidom.py behaviour that complies with the DOM Level 1 REC,
    which says that when a node newChild is added to the tree, "if the
    newChild is already in the tree, it is first removed."

    pulldom.py is patched to use the public minidom interface instead
    of setting .parentNode itself.  Possibly this reduces pulldom's
    efficiency; someone else will have to pronounce on that.