[m-dev.] trivial diff: define `int:is/2' in Mercury

[Simon Taylor]

> > library/int.m:
> > 	Define `int:is/2' in Mercury. It was defined in C to avoid
> > 	complaints from Prolog compilers.
> 
> Shouldn't you do the same for float:is/2?

There's no such predicate.
It could be argued that `int:is/2' should be made obsolete
and removed in a later release.
It might be worth adding `:- pred std_util:id(T, T).' as a replacement.

Simon.