XPath requires that the namespace nodes are linked to an Element.
JDOM does not have such a relationship, so we improvise.
Jaxen uses the identity equals ( == ) when comparing
one 'node' to another, so we have to make sure that within the context of
Jaxen we always return the same instances of NamespaceContainer each time.
Further, for jaxen the instance of a Namespace for one Node cannot be the
same instance of the same Namespace on a different Node...
This all also means that all Jaxen interaction is done with NamespaceContainer
and not the JDOM Namespace, which in turn means that when Jaxen returns
a NamespaceContainer node, it has to be unwrapped to a simple Namespace.