[OCaml] Fix the dynamic_cast test

Add out typemaps for SWIGTYPE *DYNAMIC and SWIGTYPE &DYNAMIC.

Add dynamic_cast_runme.ml.

Examples/test-suite/ocaml/dynamic_cast_runme.ml

@@ -0,0 +1,9 @@
+open Swig
+open Dynamic_cast
+
+let f = new_Foo '()
+let b = new_Bar '()
+
+let x = f -> blah ()
+let y = b -> blah ()
+assert (_do_test '(y) as string = "Bar::test")

Lib/ocaml/typemaps.i

@@ -307,6 +307,11 @@ SIMPLE_MAP(unsigned long long,caml_val_ulong,caml_long_val);
     $2 = ($2_ltype) caml_string_len($input);
 }
 
+%typemap(out) SWIGTYPE *DYNAMIC, SWIGTYPE &DYNAMIC {
+    swig_type_info *ty = SWIG_TypeDynamicCast($1_descriptor, (void **)&$1);
+    $result = SWIG_Ocaml_ptr_to_val("create_$ntype_from_ptr", (void *)$1, ty);
+}
+
 /* Array reference typemaps */
 %apply SWIGTYPE & { SWIGTYPE ((&)[ANY]) }
 %apply SWIGTYPE && { SWIGTYPE ((&)[ANY]) }