pfft: remove unwritten tests
pnfft: add a few casts [c2r]
pnfft: add c2c c2r compare tests
pnfft: add c2r/c2c compare tests for gradient and timer
[WARNING] This branch will be rebased (enable debug)

at the moment, r2c/c2r transforms don't work yet,
but at least c2c transforms aren't broken