__callee__ behaves differently from MRI

jruby 1.7.13 and 1.7.16.1 both in --2.0 mode

``` ruby
class Foo
    def foo
        {__method__ => __callee__}
    end
    alias bar foo
end
raise 'fail' if Foo.new.foo == Foo.new.bar
```

They must not be equal.
