pnfft: fix init_x_3d_adv

would always produce x > x_max
pnfft: tests: use pnfft_init_x_3d{,_adv}
pnfft: allow tests to be run from any directory
pnfft: add function for debug printing
pnfft: store fourier coefficients as R*
pnfft: store pfft input as R*
pfft: add apr_real_3d for printing real 3d-arrays
pnfft: add apr_real_3d for printing real 3d-arrays
pnfft: simple test: for c2r
pnfft: add test to check c2r error
pnfft: add define for c2r transform
pnfft: C2R
pnfft: test_adv_c2r: make local_M big enough for c2r
pnfft: don't support c2r transform with transposed input for now
pnfft: use less processes for c2r test
pnfft: correctly initialize c2r test data
pfft: properly support c2r as PFFT_FORW and r2c as PFFT_BACK
pfft: add c2r test
debug printf
pfft: add c2r over/undersample test