code: public String verboseToString() {
          String out = resultToString(getResult());
          switch (result) {
          case BACK:
          case FAIL:
              out = out + vertex.throwableToString();
              break;
          case FOLLOW:
          case SUCCEED:
              out = out + vertex.moreToString();
              break;
          case POSSIBLE:
              break;
          default:
              break;
          }
          out = out + "Certificate contains:\n" + vertex.certToString();
          return out;
      }
docs: return a string representation of this build step, showing all detail of
  the vertex state appropriate to the result of this build step, and the
  certificate contents.
  
  @returns String