Update todd_coxeter.C

Fixed: variable redefinition.
Patched func: Graph::Graph(const int *cartan,
             const std::vector<Word>& gens, //namesake
             const std::vector<Word>& v_cogens,
             const std::vector<Word>& e_gens,
             const std::vector<Word>& f_gens,
             const Vect& weights)