Compares the file checksum with the value of the checksum file.
# S3 method for GenericDataFile
compareChecksum(this, ...)Returns TRUE if the file checksum is identical to the stored value
  in the corresponding checksum file, otherwise FALSE.  FALSE is
  also returned if the checksum file does not exist.
  An exception is thrown if the file does not exist.
Additional arguments passed to *validateChecksum().
Henrik Bengtsson
*validateChecksum().
  *readChecksum().
  *writeChecksum().
  *getChecksum().
  For more information see GenericDataFile.