If you parse a namespaced document with Crimson
and write it out, it works. But if you use
createDocument and write it out, the namespace is
omitted.

org.apache.crimson.tree.ElementNode2.writeXml has:

        // ...
	out.write (tagStart, 0, 1);	// "<"
	out.write (qName);
        // ...

I.e. it does not even try; probably it only works
after a parse due to the 'xmlns' pseudoattr being
serialized back as is.

Xerces (XMLSerializer) works fine.

XMLUtil therefore needs to refuse to use Crimson's
serializer when any element in the document has a
namespace. It can use Xerces if available.