I was looking for a Julia package to handle rational functions, when I
noticed that the `Polynomials` package implements `gcd`, `div`, and `rem`.
So it would be possible to simply use `Rational{Poly}`... or so I thought.
Unfortunately, the type `Rational` prevents this use, since it requires its
type parameter to derive from `Integer`.
I think it would be more in line with Julia's goal of polymorphism if
`Rational` "just worked" with any Euclidean domain. Is there some
justification for the current behaviour, or should I file this as a issue
(or make a pull request)?
