(which was actualy already there for the diameter)

the same as the one used in State.to_string (in state.ml)

This is necessary  to compute the heigth in a  tree and will probably
be useful for other purposes

Add neigh type (struct composed of state, reply and weight), add 3 new function for neigh type, add state.lus generation by salut, modificate unison,bfs-spanning-tree and rsp-tree (compare and kind2 work\!), add demon_is_valid function, a new constant (liste of neighbors number), modificate algo for the new to_state function

+ finish/fix the k-clustering algo
+ add it in the non-reg test list