T5: clusters are not sorted by size by default

[rhjohnstone]

Cell 17:

print ('Ten molecules from second largest cluster:')
# Draw molecules
Draw.MolsToGridImage([mols[i][0] for i in clusters[1][:10]], 
                     legends=[mols[i][1] for i in clusters[1][:10]], 
                     molsPerRow=5)

However, the clusters returned by Butina.ClusterData(distance_matr,len(fps),cutoff,isDistData=True) are not sorted by default, i.e. we cannot guarantee that clusters[1] is indeed the second largest cluster.

In the talktorial, it does happen that (at least) the first two clusters are correctly ordered, but when I was using a different original target, the second cluster only had one element, while others had more. Anyway, this is easily checked by just listing the lens of the clusters. Moreover, the docs do not claim that they are ordered.