request support for more types when casting

This is a formal comment on section 17.1 or SPARQL 1.1 Query
http://www.w3.org/TR/2013/REC-sparql11-query-20130321/#operandDataTypes <http://www.w3.org/TR/2013/REC-sparql11-query-20130321/#operandDataTypes>

I was recently disappointed that xsd:date was not in the first list of supported datatypes (for casting), i.e.
xsd:integer <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-integer>
xsd:decimal <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-decimal>
xsd:float <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-float>
xsd:double <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-double>
xsd:string <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-string>
xsd:boolean <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-boolean>
xsd:dateTime <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/#dt-dateTime>

I am using strdt() as a workaround. When this recommendation is next reviewed I request that this list be expanded (at least to include xsd:date), but maybe to include all primitive datatypes (perhaps except xsd:duration which is specifically difficult)

Jeremy