OpenID must use canonical ID when authenticating XRI i-names

Issue Summary

I-name aliases don't seem to work.

From OpenID Authentication 2.0 - Final :: Appendix A.5. XRI CanonicalID:

...if the XRI i-names =example and =exmpl both yield an XRDS document with the CanonicalID xri://(example)!1234 then those Identifiers should be treated as equivalent. For applications with user accounts, the persistent Canonical ID xri://(example)!1234 should be used the primary key for the account. Although the i-names =example and =exmpl may also be stored for reference as display names, they are reassignable identifiers and should not be used as persistent keys.

This is one of the reasons I prefer XRI i-names to OpenID URLs: URLs can be transferred when bought or sold, as can the human-readable part of an i-name. But the canonical ID of an i-name - the i-number - is persistent and always represents the same identity.

(I'll also see if I can rustle up a patch...)