Independent test of grid factoring methods.

To address #258, we are making changes to allow 1 values in grid_shape. Previously, we had two methods for computing the factors, I think one slow but simpler, and one fast and more subtle. Only the second one of these is surviving the refactor for this, as the first is effectively unused code. But, the deprecated method being removed might be useful as an independent test of the factorization method that we do use. This deprecated method proved difficult to adapt to allowing the 1 values, which also argued for its removal.

But in case this alternate method is later useful for testing, I note the code used here, so it is not lost track of.

```
def test_both_methods(self):
"""
Do the two methods of computing the multiplicative partitions agree?
"""
for s in [2, 3]:
for n in range(2, 512):
self.assertEqual(utils.mult_partitions(n, s),
utils.create_factors(n, s))

def divisors(n):
i = 2
while i>> mult_partitions(52,3)
[(2, 2, 13)]
>>> mult_partitions(52,2)
[(2, 26), (4, 13)]
"""
return [tuple(flatten(p)) for p in mult_partitions_recurs(n,s)]

def mult_partitions_recurs(n, s, pd=1):
if s == 1:
return [n]
divs = divisors_minmax(n, pd, int(sqrt(n)))
fs = []
for d in divs:
fs.extend([(d,f) for f in mult_partitions_recurs(n/d, s-1, pd)])
pd = d
return fs
```

Commencez par localiser l’implémentation actuelle de multiplicative-partition et vérifier si les helpers create_factors obsolètes sont toujours présents après le refactoring de grid_shape. Comparez les deux approches décrites dans l’issue, puis déterminez si un test indépendant peut couvrir la méthode restante, y compris les formes de grille contenant des valeurs 1 ; le travail est considéré comme terminé lorsque le test est utile et réussit pour les cas pris en charge.

Rédigé par le modèle d'indexation à partir du texte de l'issue.