N3 to RDF/XML conversion generating bad 'xmlns' declarations

Hi,

If I try to do 'cwm.py --n3 resto.n3 --rdf' with the following file :

 http://nospum.net/resto.n3

cwm will generate RDF/XML with bad xmlns declarations. Specifically,
stuff like this :

 # @prefix foo: <x-urn:foo.com#> .
 # equivalent N3 'foo:bar "baz";'

 <bar xmlns="foo:">baz</bar>

I poked around the code a bit and added a patch (attached) to
XMLWriter.figurePrefix in notation3.py -- I am not intimate with
everything that goes on in cwm-land so perhaps there is a more elegant
way to handle this.

Cheers,