CD-1 issue #20: multiple node identities

The issue number refers to the XLS-sheet found in this email:
http://lists.oasis-open.org/archives/xacml/200909/msg00013.html

The commenter states that multiple resource-id attributes are not 
meaningful for XML documents.

However, the section is not specific to XML documents and in a general 
case a node may have multiple identities so no restriction should be done.

I propose that we make no change.

Best regards,
Erik