Fix IGF result not being taken modulo N
Fix IGF result not being taken modulo N

jquesnelle/libntru,iblumenfeld/libntru,jl777/libntru,iblumenfeld/libntru,jquesnelle/libntru,jquesnelle/libntru,jl777/libntru,jl777/libntru,iblumenfeld/libntru