put back changes removed in sha: 1cb82084 and sha:76c21c6e

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 !

Update: add the previous state in argument of the fault function.

New: add a fault functions to the Algo (to inject fault when a legitimate configuratiuon is reached).

nb: I needed to  split Main to avoid a Module self-loop  (as I need to
use do_step in Daemon).

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)

Its basename is the basename of the name of the .dot file.

Also provide a =--gen-register= option generates such a registring ml
file. --gen-register also generate a state.ml skeleton file.

The Makefile test/Makefile.inc also suppose that the types of the state
is defined in state.ml