Heat 1 teaspoon of the oil in a large saucepan. Add the onion and salt and cook over moderately low heat, stirring, until the onion softens, about 8 minutes. Add the curry and cinnamon stick and cook for 1 minute. Stir in the sugars and vinegar and bring to a boil. Add the mangoes and cook, stirring occasionally, until softened, 35 to 40 minutes. Add the cranberries and cook over moderate heat for 40 minutes, crushing them against the sides of the pan.