Metadata extension proposal/namespace

Per the focus call, I'd like to bring this document for a vote:

http://www.oasis-open.org/committees/download.php/11805

This is a small proposal for an extension role to cover the stand-alone
attribute query use case. It also covers any case where SAML attribute
queries are composed with a non-SAML-specific profile, so it's fairly
important to get a common extension for it, I think.

The XML namespace is currently:

	urn:oasis:names:tc:SAML:metadata:extension

This isn't that far off what Eve was tossing around, but tweaking it would
be no big deal. I personally don't think a version number needs to be in it,
but if we had one, I think it belongs at the end, not in the middle.

I'd maybe propose something like:

	urn:oasis:names:tc:SAML:metadata:ext:attrreq

With regard to the CD draft of the SAML 1.x metadata, we could alter it by
changing the namespace to match this convention as well, and then vote a
second CD.

-- Scott