Rigid foam board in walls between studs, plus fiberglass batt?
I am doing exactly this, but the reason for the rigid foam is to create an air channel along the underside of the roof to allow airflow up to the ridge vent. The layering is, from the outside inwards, roof, 1 in. airspace, rigid foam, batts, vapor barrier (plastic), drywall. 

Understand that the function of the vapor barrier is to prevent moisture from migrating from the warm side into the total thickness of insulation towards the cold side, where at some point the temperature gradient will drop enough to cause condensation. You do NOT want this to occur inside the insulation. The fact that the rigid foam is also a vapor barrier is not a problem as long as you have a correct barrier immediately behind the drywall.

If by "adding batt inside" you meant "inside the wall - towards the roof", then I would not rely on the rigid foam acting as a sufficient vapor barrier unless you made a point of carefully sealing all the edges with Acousiseal. Preventing air migration past the insulation is critical to its effectiveness, and you must also provided for ventilation of the roof material itself.