nonNegativeInteger datatype recognition

[nevenavv]

XSD's nonNegativeInteger datatype was not supported and when parsing document with such datatype, and then working with it's triples would give following exception (Jena backend):

java.lang.RuntimeException: java.lang.IllegalArgumentException: No matching field found: lexicalValue for class java.lang.Integer

Simple example:

File: simple.rdf

<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:j.0="http://test.com/" > 
  <rdf:Description rdf:about="http://test.com/a">
    <j.0:b rdf:datatype="http://www.w3.org/2001/XMLSchema#nonNegativeInteger">1</j.0:b>
  </rdf:Description>
</rdf:RDF>

test:

(def model (document-to-model (java.io.FileInputStream. "simple.rdf") :xml))
(def triples (model-to-triples model))
(count triples)
=> Exception