Cross-crate stability attributes on tuple structs are ignored

[dmanescu]

In file test_experimental.rs:

#[deny(experimental)];
extern mod test_experimental_crate;

fn main() {
    let _ = test_experimental_crate::Struct { x: 1 };
    let _ = test_experimental_crate::Tuple(1);
}

In file test_experimental_crate.rs:

#[experimental]
pub struct Struct { x: int }

#[experimental]
pub struct Tuple(int);

Compiler issues this:

test_experimental.rs:15:13: 15:38 error: use of experimental item
test_experimental.rs:15     let _ = test_experimental_crate::Struct { x: 1 };
                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test_experimental.rs:11:8: 11:20 note: lint level defined here
test_experimental.rs:11 #[deny(experimental)];
                                            ^~~~~~~~~~~~
error: aborting due to previous error