[relax-ng] RDF spec from W3C uses RELAX NG

See "RDF/XML Syntax Specification (Revised)" at:

	http://www.w3.org/TR/rdf-syntax-grammar/

This spec contains a schema in RELAX NG (to be precise, in James' syntax), 
but does not contain a W3C XML Schema schema.

Cheers,

Makoto