INT 15 - Rational Systems DOS/4GW - ???
AX = BF04h
BX = PSP segment of extender
Return: nothing???
Notes:  if BX is not the PSP segment of the extender, it passes the call down
the INT 15 chain; this allows nested instances of the extender
grabs INT 2Fh and installs handlers for INT 2F/AX=1605h-1607h

See also: 2F1607BX22C0

15BF04 - Rational Systems DOS/4GW - ???