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.
