Small fixes for optimisation stage
Small fixes for optimisation stage

tias/libminizinc,tias/libminizinc,nathanielbaxter/libminizinc,jjdekker/libminizinc,nathanielbaxter/libminizinc,jjdekker/libminizinc,jjdekker/libminizinc,jjdekker/libminizinc,nathanielbaxter/libminizinc,nathanielbaxter/libminizinc