commented out unsound "lfp"/"gfp" handling + fixed set output syntax;
the "lfp"/"gfp" bug can be reproduced by looking for a counterexample to
lemma "(A \<union> B)^+ = A^+ \<union> B^+"
Refute incorrectly finds a countermodel for cardinality 1 (the smallest
counterexample requires cardinality 2).
make Nitpick output everything to tracing in debug mode;
so that when an exception occurs, I can switch to the tracing window to see what was in the response window before the exception blew everything away