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

The previous  scheme was to  define everything  that is common  to all
user nodes in  a file named state.ml. This file was supposed to define
the algo  state type,  as well  as optional  functions such  as fault,
legitimate, or potential.

But in  order to be  able to define,  say, a legitimate  function that
uses user  nodes (which is the  case for dijkstra token  ring) without
introducing any dependency loop, it  is necessary to split state.ml in
two modules.

The new module is called Config (config.ml).

nb: I had to modify the GenSessions module in rdbg to reflect this change !

To force that, I've changed the Register interface (and thus GenRegister)

The rationale is that:
- in lurette mode, they should be the same for all algos already
- in batch mode, action declarations are ignored anyway (except in custom mode)