order of endpoints of edges in ``yen_k_shortest_simple_paths`` algorithm.

[kappybar]

In the first test of sage.graphs.path_enumeration.yen_k_shortest_simple_paths , the following resut appears.

from sage.graphs.path_enumeration import yen_k_shortest_simple_paths
sage: g = Graph([(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 5, 2),
....:            (5, 6, 100), (4, 7, 3), (7, 6, 4), (3, 8, 5),
....:            (8, 9, 2), (9, 6, 2), (9, 10, 7), (9, 11, 10),
....:            (11, 6, 8), (10, 6, 2)])
sage: list(yen_k_shortest_simple_paths(g, 1, 6, report_edges=True, labels=True, by_weight=True))
[[(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (6, 7, 4)],
...

I don't think the last edge being (6, 7, 4) is intuitive. In considering the order of edges and consistency of results of other shortest simple path algorithms, (7, 6, 4) will be better. This fix is easy. Thus if it is ok, I will fix it.

[dcoudert]

I agree that this is misleading. You can fix that.