Heat the vegetable oil in a nonreactive medium saucepan. Add the onion and cook over moderate heat, stirring, until translucent, about 7 minutes. Add the bananas and cook, stirring occasionally, for 5 minutes. Add the mango, orange juice, brown sugar, curry powder and season with salt and pepper. Cook, stirring, until thickened, about 5 more minutes. Remove from the heat and stir in the vinegar and 1/3 cup of the lime juice, adding more to taste. Serve warm or at room temperature.