Support for XML literals

[robstewart57]

This bug is identified by the conformance-xml-example09 test.

comparing-graphs:                                                       FAIL
        Exception: user error (Graph xml-example09 not equivalent to expected:
        Expected:
          Triple (UNode "http://example.org/item01") (UNode "http://example.org/stuff/1.0/prop") (LNode (TypedL "<a:Box xmlns:a=\"http://example.org/a#\" required=\"true\">\n         <a:widget size=\"10\"></a:widget>\n         <a:grommit id=\"23\"></a:grommit></a:Box>\n    " "http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral"))
        Found:
          Triple (UNode "http://example.org/item01") (UNode "http://example.org/stuff/1.0/prop") (LNode (TypedL "<a:Box required=\"true\">\n         <a:widget size=\"10\"></a:widget>\n         <a:grommit id=\"23\"></a:grommit></a:Box>\n    " "http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral"))
        )

See https://travis-ci.org/robstewart57/rdf4h/jobs/540783693#L1739 .

[robstewart57]

This is being handled upstream in the xmlbf library: https://gitlab.com/k0001/xmlbf/merge_requests/9 .

[robstewart57]

Could the failing test (https://github.com/robstewart57/rdf4h/blob/master/data/xml/example09.rdf) be added upstream to somewhere in https://github.com/w3c/rdf-tests/tree/gh-pages/rdf-xml ?