INT 21 U - DOS 4+ - COMMIT FILE
        AH = 6Ah
        BX = file handle
Return: CF clear if successful
            AH = 68h
        CF set on error
            AX = error code (06h) (see AH=59h)
Note:   identical to AH=68h in DOS 5.0; not known whether this is the case in
          DOS 4.x