Boil chicken legs and breasts in 2-½ quarts water with onions, celery stalk, and salt. Simmer slowly for 1-½ hours. Cool in broth. Put ¾ cup water in a small pan; sprinkle in gelatin and stir over low heat until just dissolved. Cool for 30 minutes. Stir mayonnaise. into gelatin. Blend well and set aside. Remove chicken from broth; bone to get about 2 cups of meat (equal portions of light and dark). Add chopped celery and mixed vegetables. Combine chicken, vegetables, and mayonnaise mixture thoroughly Add salt and pepper to taste. Stir in drained pineapple and pecans. Wet a 2-quart mold. If desired, arrange sliced stuffed olives on the bottom to make a pattern when the aspic is inverted. Spoon in the chicken mixture carefully and chill until firm. Unmold and serve.