Combine raisins and water in a small saucepan. Boil 5 minutes. Blend brown sugar, cornstarch, cinnamon, and salt together; add to hot raisins. Cook and stir until syrup is clear. Remove from heat, and stir in vinegar and butter or margarine. Cool slightly.
Turn filling into a pastry lined pan. Cover with top crust. Seal edges, and cut slits in the top crust.
Bake at 425 degrees F (220 degrees C) for 30 to 35 minutes.