Fix t_impulse_offset test for FFT for QC>=2.9
Fix t_impulse_offset test for FFT for QC>=2.9

Fixes #97

> In the latest QuickCheck, t_fftInverse will only be tested 1
> time, not 100. This is because QuickCheck now assumes that
> any property without a forAll (or similar) is deterministic.
>
> The easiest way to fix it is to use a normal quantifier
> instead of MkProperty. Using the Blind modifier you can
> get something that doesn't need a Show instance, which
> won't break in the future:

Shimuuar/statistics,bos/statistics,Shimuuar/statistics,bos/statistics