[OCaml] Fix possible GC issues in generated director code

Make `classDirectorMethod()` generate `CAMLreturn_type()` or
`CAMLreturn0` when there are local variables of type `value`.

Examples/test-suite/ocaml/director_unroll_runme.ml

@@ -0,0 +1,15 @@
+open Swig
+open Director_unroll
+
+let director_unroll_MyFoo ob meth args =
+  match meth with
+    | "ping" -> C_string "MyFoo::ping()"
+    | _ -> (invoke ob) meth args
+
+let a = new_derived_object
+  new_Foo (director_unroll_MyFoo) '()
+
+let b = new_Bar '()
+let _ = b -> set (a)
+let c = b -> get ()
+let _ = assert ((a -> "&" () as int) = (c -> "&" () as int))

Source/Modules/ocaml.cxx

@@ -1394,8 +1394,7 @@ public:
 	pure_virtual = true;
       }
     }
-
+    Printf(w->locals, "CAMLparam0();\n");
-    Wrapper_add_local(w, "swig_result", "CAMLparam0();\n" "SWIG_CAMLlocal2(swig_result,args)");
 
     /* determine if the method returns a pointer */
     is_pointer = SwigType_ispointer_return(decl);
@@ -1469,16 +1468,18 @@ public:
 
     if (ignored_method) {
       if (!pure_virtual) {
-	if (!is_void)
-	  Printf(w->code, "return ");
 	String *super_call = Swig_method_call(super, l);
-	Printf(w->code, "%s;\n", super_call);
+	if (is_void)
+	  Printf(w->code, "%s;\n", super_call);
+	else
+	  Printf(w->code, "CAMLreturn_type(%s);\n", super_call);
 	Delete(super_call);
       } else {
 	Printf(w->code, "Swig::DirectorPureVirtualException::raise(\"Attempted to invoke pure virtual method %s::%s\");\n", SwigType_namestr(c_classname),
 	       SwigType_namestr(name));
       }
     } else {
+      Wrapper_add_local(w, "swig_result", "SWIG_CAMLlocal2(swig_result, args)");
       /* attach typemaps to arguments (C/C++ -> Ocaml) */
       String *arglist = NewString("");
 
@@ -1673,6 +1674,8 @@ public:
 	  Printf(w->code, "CAMLreturn_type(*c_result);\n");
 	}
       }
+    } else {
+      Printf(w->code, "CAMLreturn0;\n");
     }
 
     Printf(w->code, "}\n");