Go back between two stages of the Edmond's algorithm
stepbackArbor function rebuilds an arborescence
present in earlier stage of Edmonds's algorithm to find a
minimum cost arborescence.
list with elements of the previous stage
list with elements of the next stage
A updated list of elements of the earlier stage with a new arborescence
This function is an auxiliar function used in msArborEdmonds and getMinimumArborescence.