Change default value of warm_restart to false.

When creating a Context, sane default values are assigned
to a number of options, including the warm_restart.
To be conservative with respect to old behaviour,
the warm restart is set to false by default.

src/Context.cpp

@@ -11,7 +11,7 @@
 ContextData::ContextData(ProblemData* pb)
 : it_num(0), UB(exp10(10)), feasible_solution_set(nullptr), problem(pb),
   T_test(0.0), T_model(0.0), T_relaxation(0.0), T_homo(0.0), T_screening_computation(0.0),
-  T_screening_method(0.0), nbr_iter(0), itmax(0), cut(0), warm_restart(true),
+  T_screening_method(0.0), nbr_iter(0), itmax(0), cut(0), warm_restart(false),
   BBNodeNum(0), BestNodeNum(0), TimeBBMax(1000), nbr_update_Bsupp(0), T_best_Bsupp(0.0),
 #ifdef USE_CPLEX
   CplexNodeNum(0), CplexStatus(IloAlgorithm::Status::Unknown), cplex_branching_rule(1),