yaml: use C classes for dump/load if available
yaml: use C classes for dump/load if available

nismod/smif,tomalrussell/smif,nismod/smif,willu47/smif,tomalrussell/smif,willu47/smif,nismod/smif,tomalrussell/smif,willu47/smif,nismod/smif,willu47/smif,tomalrussell/smif