[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/primitive_ref_runme.ml

@@ -0,0 +1,20 @@
+open Swig
+open Primitive_ref
+
+let _ =
+  assert (_ref_int '(3) as int = 3);
+  assert (_ref_short '(3) as int = 3);
+  assert (_ref_ushort '(3) as int = 3);
+  assert (_ref_long '(3) as int = 3);
+  assert (_ref_ulong '(3) as int = 3);
+  assert (_ref_schar '(3) as int = 3);
+  assert (_ref_uchar '(3) as int = 3);
+  assert (_ref_float '(3.5) as float = 3.5);
+  assert (_ref_double '(3.5) as float = 3.5);
+  assert (_ref_bool '(true) as bool = true);
+  let arg = C_char 'x' in
+  assert (_ref_char '(arg) as char = 'x');
+  assert (_ref_over '(0) as int = 0);
+  let a = new_A '(12) in
+  assert (_ref_over '(a) as int = 12);
+;;