Test test functions with wrong solutions

[ocaml-sf]

Test test functions with wrong solutions

[AltGr]

That would indeed be nice: you can at the moment test manually, or each wrong solution of each exercise, but integrating that into the build would be useful.

Note that the learn-ocaml grade interface has improved a bit since #58: the results and score are now printed by default!

So the functionality would be roughly that of this script:

set -e
for wrong in $EXERCISE_DIR/wrong_solution_*.ml;  do
  ! learn-ocaml grade -e $EXERCISE_DIR -s $wrong
done

Note that, for this, we should probably disable the random input part of all expect tests, so that you are sure to catch the failures you want to no matter what the sampler gives.