Modify chef_db:fetch_requestor to support no org.

fetch_requestor has been modified to directly fetch the user record in
absence of a valid org, without first attempting to fetch a client.
Consistently update pubkey_version, since this is now part of chef_user.
Merge pull request #52 from opscode/mp/user-endpoint

Note that compatible chef_db is now under branch "mp/users-lock", which erchef has been configured to use for OSC.