Check whether the given object is a CPORetrafo object.
is.retrafo(x)[any] The object to check.
TRUE if x has class CPORetrafo, FALSE otherwise.
Other retrafo related: CPOTrained,
  NULLCPO, %>>%,
  applyCPO, as.list.CPO,
  clearRI, getCPOClass,
  getCPOName,
  getCPOOperatingType,
  getCPOPredictType,
  getCPOProperties,
  getCPOTrainedCPO,
  getCPOTrainedCapability,
  getCPOTrainedState,
  makeCPOTrainedFromState,
  pipeCPO, print.CPOConstructor