added tests for rdf.rdf_datatype.RdfDatatype
added test for rdf.rdf_datatype.RdfDatatypeBase
added tests for rdf.rdf_datatype.RdfDatatypeLabel
added tests for rdf.rdf_datatype.TypedValue
changed throw '..' to throw new Error('..') in RdfDatatype
removed unneeded commas
fixed binding of function call in DatatypeLabel tests