[Ironruby-core] Fixnum Patch

[John Messerly]

Peter Bacon Darwin:

> I have now tested it and if you have a method that, for instance,
> returns int? then on the occasions that null is returned that class of
> the resulting object is NilClass and when it is not null, the class is
> Fixnum.  So all seems to be well and I am happy to fix-up those methods
> in Bignum and Fixnum that should use Nullable types when I next submit
> a patch.

I love it when stuff just works :)

- John