CALL BPX1ITY, Determine if device is a TTY +
(=A(STDOUT_FILENO), Input: File descriptor +
RETVAL), Return value: 0 isn't, 1 is +
VL,MF=(E,PLIST) ----------------------------------
ICM R15,B'1111',RETVAL Test RETVAL
BZ PSEUDO RETVAL=0 means device not terminal