subst_auxvar.m: account for auxiliary type 5

Fixes crashes in model_info with differentiate_forward_vars

matlab/subst_auxvar.m

@@ -59,8 +59,8 @@ if ~isempty(aux_index)
             % Expectation operator
             str = sprintf('%s', M_.aux_vars(aux_index).orig_expr);
             return
-        case 6
-            % Ramsey's multipliers
+        case {5,6}
+            % differentiate_forward_vars and Ramsey multipliers
             if ~isempty(aux_lead_lag)
                 str = sprintf('%s(%d)', M_.endo_names{M_.aux_vars(aux_index).endo_index}, aux_lead_lag);
             else

tests/differentiate_forward_vars/RBC_differentiate_forward.mod

@@ -88,6 +88,7 @@ end;
 
 steady;
 check;
+model_info;
 
 perfect_foresight_setup(periods=500);
 perfect_foresight_solver;