Add a typeassert in normalization

`Int(x)` does no longer wrap `convert(Int, x)::Int`, so the type
assertion has be added manually to ensure inferability. Fixes
JuliaMath/FFTW.jl#57.

Author: martinholters

src/definitions.jl

@@ -255,7 +255,7 @@ summary(p::ScaledPlan) = string(p.scale, " * ", summary(p.p))
 *(p::Plan, I::UniformScaling) = ScaledPlan(p, I.λ)
 
 # Normalization for ifft, given unscaled bfft, is 1/prod(dimensions)
-normalization(T, sz, region) = one(T) / Int(prod([sz...][[region...]]))
+normalization(T, sz, region) = one(T) / Int(prod([sz...][[region...]]))::Int
 normalization(X, region) = normalization(real(eltype(X)), size(X), region)
 
 plan_ifft(x::AbstractArray, region; kws...) =