Graceful termination when getPrimalRays is not implemented

[kibaekkim]

When some subproblem is dual infeasible, DSP tries to use an extreme ray. However, getPrimalRays is not implemented in most solvers in Osi (except for Cplex as far as I checked).

DSP/src/Solver/DantzigWolfe/DwWorker.cpp

Line 276 in 41c3586

std::vector<double*> rays = osi_[s]->si_->getPrimalRays(1);

If getPrimalRays is implemented, a bundle cut may be generated by using the extreme ray of the dual infeasible subproblem. Otherwise, we would better return a message and terminate DSP gracefully.

Originally posted by @hideakiv in #211 (comment)