pub/priv qualifiers on individual variants

```
use foo::{f, h};

mod foo {
    pub enum f {
        pub g,
        priv h
    }
}


fn main() {
    let y = h;
}
```

This shouldn't compile, because `h` is private. But it's currently accepted. I'm not sure if we want to support pub/priv on variants or not, but if not, we should disallow pub/priv on them altogether.
