PERF: Use a std::deque instead of std::list to store the support window.
ENH: Get spectra filter inputs.
BUG: USE_FFTWD -> ITK_USE_FFTWD.
ENH: Replace Legaldim with VnlFFTCommon::IsDimensionSizeLegal.
STYLE: Style improvements for itkVnlFFT1DRealToComplexConjugateImageFilter.