Sect 6.2.5 - allow XRD

From Yadis

In Section 6.2.5 the note states ".... the response MUST be of type 1 or 2."

In the absence of an Accept header, the web server may still return an XRDS document if it was asked for an XRDS document. We feel that a response with a content-type of application/xrds+xml is valid.

Done.