[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/catches_runme.ml

@@ -0,0 +1,39 @@
+open Swig
+open Catches
+
+let _  =
+  try
+    ignore (_test_catches '(1)); assert false
+  with Failure s ->
+    assert (s = "C++ int exception thrown, value: 1")
+
+  try
+    ignore (_test_catches '(2)); assert false
+  with Failure s ->
+    assert (s = "two")
+
+  try
+    ignore (_test_catches '(3)); assert false
+  with Failure s ->
+    assert (s = "C++ ThreeException const & exception thrown")
+
+  try
+    ignore (_test_exception_specification '(1)); assert false
+  with Failure s ->
+    assert (s = "C++ int exception thrown, value: 1")
+
+  try
+    ignore (_test_exception_specification '(2)); assert false
+  with Failure s ->
+    assert (s = "unknown exception")
+
+  try
+    ignore (_test_exception_specification '(3)); assert false
+  with Failure s ->
+    assert (s = "unknown exception")
+
+  try
+    ignore (_test_catches_all '(1)); assert false
+  with Failure s ->
+    assert (s = "unknown exception")
+;;