f, fshift log to file after first kernel run

f and fshift arrays are written to file after the first kernel
execution.

For the OpenCL version. the results are also compared to the CUDA
results, if the corresponding files are found.

OpenCL: see
#define DEBUG_DUMP_F_OCL
#define DEBUG_DUMP_FSHIFT_OCL
Output files: ocl_f.txt and ocl_fshift.txt

CUDA: see
#define DEBUG_DUMP_F_CUDA
#define DEBUG_DUMP_FSHIFT_CUDA
Output files: cuda_f.txt and cuda_fshift.txt