as many  new local  variables as necessary  so that an  expression is
made at most of one operator.

The rational  for that  is to obtain  a lic  code that is  trivial to
clock check (nested node calls, for example, make it less simple).

The old behavior can still be obtained using --keep-nested-calls.

During  that  change,   I  realised  that  I  did   not  clock  check
asserts. Hence, I have also added this check.

clock_info, and  therefore also  remove clock_info. The  rationale of
this  change is  that  it  makes things  slightly  simpler, and  more
homogeneous with what is done in type checking.

Not yet implemented (assert false): iterators, struct

Add a UnifyClock module, and rename Unify into UnifyType.

nb : a lot of test are now broken, because
   - the clock checking is now plugged ;-)
   - iterators, struct are not yet implemented

It  does not  work, I  have changed  my mind  to use  a  more general
clocking algorithm based on  unification. I commit that current state
just in case I change my mind again...