Separating violated constraints

In this file a constraint handler checking solutions for feasibility and separating violated model constraints is implemented, as described in: "Solving the Steiner tree problem in graphs to optimality" by T. Koch and A. Martin. The separation problem for the cut inequalities described in Problem description and solving approach can be solved by a max-flow algorithm in polynomial time. Regarding the variable values of a given LP solution as capacities on the edges, one can check for each , with being the root, whether the minimal -cut is less than one. In this case, a violated cut inequality has been found, otherwise none exists. In order to calculate such a minimal cut Hao and Orlin's preflow-push algorithm is used. Furthermore, the file implements a dual ascent heuristic, based on a concept described in "A dual ascent approach for Steiner tree problems on a directed graph." by R. Wong.