[OCaml] Fix member var getters and setters

Add `membervariableHandler()` to the `OCAML` class in ocaml.cxx (it is
partly based on the code in python.cxx and octave.cxx).

In Lib/ocaml/class.swg, wrapped classes/structs were not being added
to `class_master_list`. This is fixed by adding a call to
`register_class_byname`.

Add a unit test in the form of struct_value_runme.ml.

Lib/ocaml/class.swg

@@ -56,6 +56,7 @@ begin
 	  (fun mth arg -> invoke_inner raw_ptr mth arg)
 end
 
+let _ = register_class_byname "$realname" create_$classname_from_ptr
 let _ = Callback.register 
           "create_$normalized_from_ptr"
           create_$classname_from_ptr

Lib/ocaml/swig.ml

@@ -155,5 +155,5 @@ let _ = Callback.register "swig_set_type_info" set_type_info
 let class_master_list = Hashtbl.create 20
 let register_class_byname nm co = 
   Hashtbl.replace class_master_list nm (Obj.magic co)
-let create_class nm arg = 
+let create_class nm =
   try (Obj.magic (Hashtbl.find class_master_list nm)) with _ -> raise (NoSuchClass nm)