[OCaml] Fix the handling of bools in overloaded functions

Use the SWIG_TYPECHECK_BOOL precedence level instead of
SWIG_TYPECHECK_INTEGER when checking for bools.

Add a runtime test in the form of overload_bool_runme.ml.

Examples/test-suite/ocaml/overload_bool_runme.ml

@@ -0,0 +1,15 @@
+open Swig
+open Overload_bool
+
+let _ =
+  assert (_overloaded '(true) as string = "bool");
+  assert (_overloaded '(false) as string = "bool");
+  assert (_overloaded '(0) as string = "int");
+  assert (_overloaded '(1) as string = "int");
+  assert (_overloaded '(2) as string = "int");
+  assert (_overloaded '("1234") as string = "string");
+  assert (_boolfunction '(true) as string = "true");
+  assert (_boolfunction '(false) as string = "false");
+  assert (_intfunction '(true) as string = "int");
+  assert (_intfunction '(false) as string = "int");
+;;