Add xsd datatypes xsd:dateTimeStamp, xsd:yearMonthDuration, xsd:dayTimeDuration

There are some new XSD datatypes not covered by Jena's datatype system.

• xsd:dateTimeStamp
• xsd:yearMonthDuration
• xsd:dayTimeDuration

They are all derived types. While Xerces does not directly support them (they are in XSD 1.1 final, Xerces 2.11.0 only goes as far as drafts of 1.1), they can be supported easily by inherining from the base type and fixing the URI and the parsing. Their value is one of the existing value types and they can be treated via syntactic restrictions on the lexical form.

ARQ already handles these types as values to a limited extent. Putting them into Jena core datatypes would unify the handling.