HAPI releasePool() passes bad address to cudaFreeHost()

[trquinn]

ChaNGa, using the HAPI interface to CUDA, fails at exit because cudaFreeHost() reports an invalid argument when called in the releasePool() method. From code inspection, it is apparent that, if a pool gets used, pools[i].head is not necessary the beginning of the pinned chunk created by cudaMallocHost().