Privacy can be violated using pointers

[Dretch]

When a struct is accessed via a pointer then its private fields are accessible:

mod my_mod {
    pub struct MyStruct {
        priv priv_field: int
    }
    pub fn MyStruct () -> MyStruct {
        MyStruct {priv_field: 4}
    }
}

fn main() {
    let my_struct = my_mod::MyStruct();
    let _woohoo = (&my_struct).priv_field; // compiles but shouldn't
    let _woohoo = (~my_struct).priv_field; // ditto
    let _woohoo = (@my_struct).priv_field; // ditto
    let nope = my_struct.priv_field;       // compile error as expected
}

[catamorphism]

Reproduced as of d2ad028