Fix missing XML "serialization" case for HasMember "sites".
Fix missing XML "serialization" case for HasMember "sites".

This is needed because StructuralPairs (apply/unapply) are not
sites anymore and are just HasMember.

orc-lang/orc,orc-lang/orc,orc-lang/orc,orc-lang/orc,orc-lang/orc