Immutable classes aren't considered implicitly copyable

[pcwalton]

Failing testcase:

class C {
    let x: uint;

    new(x: uint) {
        self.x = x;
    }
}

fn f<T:copy>(x: T) {
}

fn main() {
    f(C(1u));
}

[catamorphism]

Passes but produces a warning (which it shouldn't).

[catamorphism]

This is done, but I'm having trouble getting the lint flags to work right so that the test case will fail if the warning gets printed out. I think there's a bug in how lint settings work, but haven't isolated it yet.