In my last column, “Mediation: Impassible,” I gave suggestions to break through impasse.Mediators have to be able to deal with impasse, but avoidance is the best strategy. Impassible can be pretty tough and, as they say in the movie, merely difficult should be a walk in the park.One tool I’ve found really helpful is pre-mediation telephone calls. It’s great because the lawyers can just talk to you …