[OCaml] Don't use argout typemaps by default for some reference types

The OCaml module's typemaps.i supplied argout typemaps for some
reference types (e.g. int &) by default, which was unintuitive and
inconsistent when compared with other modules. The argout_ref example
depended on this, so add a typemap to argout_ref/example.i.

Add multiple runtime tests that deal with references.

Examples/test-suite/ocaml/funcptr_cpp_runme.ml

@@ -0,0 +1,13 @@
+open Swig
+open Funcptr_cpp
+
+let _ =
+  let fp = _ADD_BY_VALUE '() in
+  assert (_call1 '(fp, 10, 11) as int = 21);
+  let fp = _ADD_BY_POINTER '() in
+  assert (_call2 '(fp, 12, 13) as int = 25);
+  let fp = _ADD_BY_REFERENCE '() in
+  assert (_call3 '(fp, 14, 15) as int = 29);
+  let fp = _ADD_BY_VALUE_C '() in
+  assert (_call1 '(fp, 2, 3) as int = 5);
+;;