mshocks: better match to the semantics given in the manual

Ensure that the block is always interpreted multiplicatively relative to the
steady state, and not relative to the pre-existing shock value (if there was
already a shock declared for the same exogenous and period(s)).

matlab/perfect-foresight-models/make_ex_.m

@@ -89,13 +89,13 @@ if isfield(M_, 'det_shocks')
             if ~M_.det_shocks(i).multiplicative
                 oo_.exo_simul(k,ivar) = v;
             else
-                oo_.exo_simul(k,ivar) = oo_.exo_simul(k,ivar) .* v;
+                oo_.exo_simul(k,ivar) = oo_.exo_steady_state(ivar) * v;
             end
         else
             if ~M_.det_shocks(i).multiplicative
                 oo_.exo_det_simul(k,ivar) = v;
             else
-                oo_.exo_det_simul(k,ivar) = oo_.exo_det_simul(k,ivar) .* v;
+                oo_.exo_det_simul(k,ivar) = oo_.exo_det_steady_state(ivar) * v;
             end
         end
     end

matlab/perfect-foresight-models/perfect_foresight_with_expectation_errors_setup.m

@@ -78,7 +78,7 @@ else
             if ~M_.det_shocks(i).multiplicative
                 oo_.pfwee.shocks_info(exo_id, prds, 1) = v;
             else
-                oo_.pfwee.shocks_info(exo_id, prds, 1) = oo_.pfwee.shocks_info(exo_id, prds, 1) .* v;
+                oo_.pfwee.shocks_info(exo_id, prds, 1) = oo_.exo_steady_state(exo_id) * v;
             end
         end
     end