Suboptimal solution found if there are redundant arcs

[barrybecker4]

I'm not sure if the original paper claims to handle this case or not, but I noticed that the scala version does not find the shortest paths if there are redundant arcs between some nodes. The reason seems to be that it does not necessarily select the shortest arc if there are more than one to select from.

See test "Find 3 the shortest paths in a graph 'test_50_2' from 0 -> 7" in my fork where I have added a test case to demonstrate.