- fixed bug in is_solution_optimal_for_auxiliary_problem() where in case of
a slack variable tau_aux was not incremented but set (= instead of +=)
- fixed bug in is_solution_optimal_for_auxiliary_problem() in which the special
artificial variable was not ignored even if it droped down to zero (and
therefore MUST be ignored)
- fixed bug in update_1() where feasibiliy does not always hold (in theory, it
does, but as documented, is_solution_feasible() need not return true); now
the assertion is only checked at certain times
- fixed several typos in comments