Of course this is only useful for algo that compute some kind of trees (more
specifically, this only work if the state contains a variable named "par" !)

Moreover, it was not taking into account whether the graph was directed or not.

The  rationale is  that the  Algo.spid that  gave processes  access to
their pid via their neighbors was a bit weird. Also, it makes the anonymity
of the algorithm more explicit: an access to the pid could appear anywhere
in the program, while now, the pid must be in state.t!

Now, if the  user needs the pid,  he must store it  explicitly in the
state via the initialization function.

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)

Indeed,  the  generated  oracle  and daemons  were  not  syntactically
correct in such cases, e.g., if an action was named "I(p)".