No WeightedGraph in current method signatures

Hello,

following a discussion on the mailing list (mainly with Simone) I am providing a small patch to "get rid" of the interface WeightedGraph in all the method signatures for the algorithms currently implemented, basically replacing it with the equally expressive Graph<V extends Vertex, We extends WeightedEdge>.

The main reason: keep it simple. So far none of the algorithms really needs the WeightedGraph interface (e.g. no need for additional methods that cannot be found in Graph). With that said I did NOT remove the WeightedGraph interface.

Hoping to meet your agreement and waiting for comments,
Ciao
Claudio