The function [delay_kont] can be used to extract the value returned
by a monad (second argument below, type `'a`).
```
  val delay_kont : string -> 'a t -> ('a ->  'a t -> 'b t) -> 'b t
```

The continuation function `(fun v mv -> ... )` can then examine
the returned value `v` and combine the monad `mv` independently,
which proves very convenient in many occasion.

The change performed by this commit permits affine (_i.e._ one or zero
effective occurrence), while linear usage (exactly one occurrence) was
mandatory before.

  + Efficient group function: sort, then group.
  + Suffix based generators:
     - generate all suffixes,
     - cross product of suffixes.

When TTHM=HA or TTHM=HD are active, HW update of the AF flag
is performed. This include the so-called "spurious" updates
that are performed independently of test code.

For efficiency reason we limit the number of such spurious
updates to what is necessary. We do so by a global
scan of the execution candidates  counting the
writes that may unset the AF flag in the final
set of effects. Notice that we also consider the
initial writes in this scan.

We perform one optimisation: by exception, when a
write effect value is the same as the value
read by the same instruction from the same location,
there is no need to add a supplementary spurious update
as the (potential) update associated to the write that
stored the value has already been counted and is sufficient.