thanks to milki for all the efforts!
Details:
- partial-copy fell afoul of BSD not having $RANDOM
- test suite: fix bad GNU sort with good perl sort
- test suite: fix md5sum dependency (which BSD doesn't have or can't
easily have or requires extra options or whatever...), by doing it
in perl. (Requires Digest::MD5, which is probably available
anyway, but since this is only for the test suite, meh!)