ADPLEXTN: (Mapped by mapping macro BLSABDPL) IPCS sets
field ADPLEFCD to ADPLEFTC (X'0003') upon entry to a TCB
exit routine to permit a common entry point to serve as a TCB exit
routine as well as one of the following types of exit routines:
ANALYZE exit routine
ASCB exit routine
Post-formatting exit routine
Verb exit routine
The registers and other conditions on entry to each of these
types of exit routines are the same. Use field ADPLEXTN to determine
the purpose of a given call to a multi-function entry point.