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.
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.