[OCaml] Re-enable the using_protected unit test

Use the [member-variable] syntax in using_protected_runme.ml as
required by the OCaml module's documentation and implementation.

Fix the return type for vec_write() in example.h in the OCaml stl
example.

Examples/ocaml/class/runme.ml

@@ -41,7 +41,7 @@ let _ = Printf.printf "    Square = (%f, %f)\n" (s -> "[x]" () as float) (s -> "
 
 let _ = print_endline "\nHere are some properties of the shapes:"
 
-let _ = List.iter (fun o -> 
+let _ = List.iter (fun o ->
   Printf.printf "    %s\n" (repr o);
   Printf.printf "        area      =  %f\n" (o -> area () as float);
   Printf.printf "        perimeter =  %f\n" (o -> perimeter () as float)