In a large frying pan, heat the butter and saute the onion, garlic, and ginger until the onion is soft, but not brown. Add the curry powder and chiles, stirring so that they do not stick or burn. Add the vinegar. There should be enough to make a smooth paste.(You may need up to 1/4 cup more vinegar.) Cover the chicken pieces with the paste and place them in a covered bowl in the refrigerator. Allow the chicken pieces to marinate for at least 2 hours. When ready to cook, place the chicken pieces in a large frying pan and add enough water to reconstitute the paste and prevent scorching. Cover and cook over low heat for 30 minutes. (You may find that you will have to add more water to prevent scorching.) After 30 minutes, add the potatoes, cover and continue to cook for an additional 15 minutes, or until the potatoes and chicken are done.