Different handling of postconditions in counterexamples.
Postconditions for that variables mentioned in these postconditions should be in counterexample are now marked with label "model_vc_post". Variables corresponding to return values are no longer handled by transformation intro_vc_vars_counterexmp. They must have location of the corresponding postcondition, label "model" or "model_trace", and label of the form "model_trace:name@result". Generartion of these labels to variables corresponding to return values created in WP is for future work.