ap.c, dp.c: exit(3) with 0 or 1, not [0, MAX_EXIT].

ap.c, dp.c: exit(3) with 0 or 1, not [0, MAX_EXIT].

Don't attempt to indicate the number of failures through the exit status
as that's too constrained.  Just stick to zero for none, and 1 for some.
Delete, the now unused, MAX_EXIT.