ICE trying to deref a newtype struct implementing Drop

```
struct S(int);

impl Drop for S {
    fn finalize(&self) {}
}

fn main() {
    *S(42);
}
```

> $ RUST_LOG=rustc=1,::rt::backtrace  rustc newtype_ice.rs 
> rust: ~"invoke at newtype_ice.rs:8:5: 8:11"
> rust: task failed at 'assertion failed: adt::is_newtypeish(repr)', /home/ben/code/repos/rust/src/librustc/middle/trans/datum.rs:722
> [...]
