Well, actually... You should never double a vapor barrier. When a wall does get wet, you could end up with moisture between the vapor barriers and it will mold before it dries. This has been an issue for homes with insulated foam board on the exterior and a vapor barrier inside. This is also the reason we don't use plastic on the exterior side of the walls. Just a few cuts in the paper from top to bottom will break the vapor barrier OR remove the paper completely.
If you want to use the paper and skip the plastic all together, tape the insulation at cuts and joints. Make sure the drywall will seal the paper to the studs and plates and caulk the bottom plate to the floor. Use tape around windows and gaskets on electrical cover plates. Make sure your weather strips on your exterior doors are sealing properly and caulk the brick moulding to the siding or use a flashing tape around windows and doors before siding.
