Support multiple targets for Suurballe

[Alpar Juttner]

The concept is that

run(s,t,k);

would do just as it does now, but in addition to it, there would be a function

init(s);

performing a full Dijkstra, which could be then followed by the of several

start(t,k);

execution, each of them would call a patrial Dijkstra to t only k-1 times.