added limits.h to values.hh so compiles with gcc
added limits.h to values.hh so compiles with gcc

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