Query errors in file input or output.

  MESSAGE = FERROR(FID,'clear') returns the error message for the

  most recent file I/O operation associated with the specified file. 

  The string 'clear' is optional.  If present, it clears the error

  indicator for the specified file.



  [MESSAGE, ERRNUM] = FERROR(FID) also returns the error number.



  FID is an integer file identifier obtained from FOPENZTI1WQ, or 0 for

  standard input, 1 for standard output or 2 for standard error.