[OCaml] Some exception improvements

The OCaml module's exception handling code was poorly designed,
gave confusing exception messages, and was vulnerable to buffer
overflows.

The OCaml module's SWIG_exception_() was adding a useless newline to
the end of the exception message.

In some cases, the integer value of f.e. SWIG_TypeError was being added
to the exception message.

The unneeded else in the OCaml module's SWIG_contract_assert() macro
was causing -Wmisleading-indentation warnings.

The OCaml module's exception handling code now mirrors that of the
Java module.

Add Lib/ocaml/std_except.i.
Add multiple runtime tests.

Examples/test-suite/ocaml/director_exception_runme.ml

@@ -0,0 +1,46 @@
+open Swig
+open Director_exception
+
+exception MyException of string * string
+
+let director_exception_MyFoo ob meth args =
+  match meth with
+      "ping" -> raise (Failure "MyFoo::ping() EXCEPTION")
+    | _ -> (invoke ob) meth args
+
+let director_exception_MyFoo2 ob meth args =
+  match meth with
+      "ping" -> (C_bool true)
+    | _ -> (invoke ob) meth args
+
+let director_exception_MyFoo3 ob meth args =
+  match meth with
+      "ping" -> raise (MyException ("foo", "bar"))
+    | _ -> (invoke ob) meth args
+
+(* Check that Failure is raised by MyFoo.ping() (via MyFoo.pong()). *)
+let a =
+  new_derived_object
+    new_Foo (director_exception_MyFoo) '()
+let a = _launder(a)
+try
+  let _ = a -> pong () in assert false
+with Failure s -> assert(s = "MyFoo::ping() EXCEPTION")
+
+let a =
+  new_derived_object
+    new_Foo (director_exception_MyFoo2) '()
+let a = _launder(a)
+try
+  let _ = a -> pong () in assert false
+with Failure s -> assert(s = "No appropriate conversion found.")
+
+let a =
+  new_derived_object
+    new_Foo (director_exception_MyFoo3) '()
+let a = _launder(a)
+try
+  let _ = a -> pong () in assert false
+with MyException (s1, s2) ->
+  assert (s1 = "foo");
+  assert (s2 = "bar");