pnfft: fix init_x_3d_adv

would always produce x > x_max
pnfft: pass correct array in assign_f_c2c
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: add support for c2r transforms with hermitean symmetry
pnfft: simple test: for c2r
pfft: properly support c2r as PFFT_FORW and r2c as PFFT_BACK
pfft: add c2r / c2c comparison tests
pnfft: add test for comparing c2c to c2r
pfft: remove unwritten tests
pnfft: add c2c/c2r comparison tests
pnfft: add c2r/c2c compare tests for gradient and timer
pnfft: fix direct pndft after c2r work
pnfft: implement c2r pndft
pnfft: add test for c2r pndft