[OCaml] Runtime tests for fvirtual, overload_polymorphic and some others

Add runtime tests for conversion, extend_typedef_class,
extend_constructor_destructor, fvirtual, overload_polymorphic,
template_rename, and using1.

Examples/test-suite/ocaml/conversion_runme.ml

@@ -0,0 +1,9 @@
+open Swig
+open Conversion
+
+let _ =
+  let bar = new_Bar '() in
+  assert (bar -> ":classof" () as string = "Bar");
+  let foo = bar -> toFoo () in
+  assert (foo -> ":classof" () as string = "Foo");
+;;