[graph-tool] Local clustering coefficient normalization

Hi Tiago, I have extensively used graph-tool, and I find it very nice and efficient so, first of all, congratulations for your work. I write to you because of a suspected bug in the local clustering coefficient, which results normalized in [0, 2] instead than in [0,1] for one of my datasets. This issue is probably due to the fact that the network was obtained by "simmetrization" of a previously directed one, by using g.set_directed(False). Best wishes.