Indeed, by using the Env.nset and Env.nget defined in
0d6575a7 a pb that was hided by the
use of Env.set and Env.get was triggered.

The bug was that variables initialisations were done several times.

In sasa.ml, the way I was updating the Env.t by iterating on the
variables was forcing to "close" expressions that were calling init
functions.

Depending on the kind of network, we should raise an exception. Indeed
such information should not be available in anonymous networks.

We will add such checks later.

with algo several actions, and allow lurette to chose them.

and reuse it for Neighbor, which make the naming more consistent.

Also add the list of neighbors to the init function. The rationale is that
to give a sensible initial value to local vars of type 'Neighbor', we need
the neighbors number.

I could have chosen to pass an integer only. Well, who can the plus
can the minus.