fft: Clean up style
fft2: FFT methods now all specify and ackn. the number of threads to use.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Merge pull request #46 from imglib/fft2-no-multithreading

fft2 package has some methods that are silently multithreaded. Enforce nThreads specification