code: public void addConstraint (Shutdowner lhs, Constraint constraint, Shutdowner rhs)
      {
          switch (constraint) {
          case RUNS_BEFORE:
              _cycle.addShutdownConstraint(lhs, Lifecycle.Constraint.RUNS_BEFORE, rhs);
              break;
          case RUNS_AFTER:
              _cycle.addShutdownConstraint(lhs, Lifecycle.Constraint.RUNS_AFTER, rhs);
              break;
          }
      }
docs: Adds a constraint that a certain shutdowner must be run before another.