CD-1 issue #36: policy without rule

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

The commenter thinks that the XACML schema should not allow a Policy 
without any rule.

I think it should allow since such a policy would simply be not 
applicable (for any sane combining algorithm) and such a policy could be 
useful as a placeholder or as output from an automatic policy compiler 
of some sort (the compiler logic could perhaps be simpler if empty 
policies are allowed).

Best regards,
Erik