Code review comment for lp:~justin-fathomdb/nova/bug740576

Thanks Brian. Yes - get_default_xmlns is the hook point at the moment. But
it's actually complicated by the fact that we don't have a 1.1 XSD yet (or
even an XML namespace?) It may be that the right place is actually in the
serialization_metadata, where you can also put an xmlns to override any
particular namespace.

I'm about to open a bug on the fact that we don't have an XML NS or XSD for
v1.1. Once we have that, the best way to handle this should be a lot
clearer, but I wanted to put in a suggested placeholder hook.

I'd like to see this land first though, because without it I can't do any
validation against the XSD schemas we do have.