7.67 cksum command is a bit "squirrely" in HPUX09

The chsum (1) command produces a different checksum on HPUX09 than HPUX10.

The 9.x cksum was defective, it did not correctly implement the POSIX
spec.  That is understandable, because the POSIX cksum spec does not
supply a test suite to easily verify an implementation is correct.

The 10.x cksum is correct.  Unfortunately that means it can not match 9.x
cksum.  A special option for 10.x "sum" was suggested to match 9.x bogus
cksum, but that did not get in.

Another implementation that did not match POSIX spec was in AIX 3.*; I
haven't checked AIX 4.* or Solaris.

Other good implementations (they give the same answer as 10.x cksum):
  - gnu cksum
  - HP Software Distributor swpackage program, on both 9.x and 10.x

Thanx to Michael Taylor (tay@cv.hp.com)