Panic: "internal compiler error: ident only path should have been covered already"

This error is triggered by providing type parameters to a generic type in a `match` pattern.

e.g.

``` rust
#![crate_type = "staticlib"]

pub struct Foo<T>(T, T);

impl<T> Foo<T> {
    fn foo(&self) {
        match *self {
            Foo<T>(x, y) => println!("Goodbye, World!")
        }
    }
}
```

[Playpen here.](http://is.gd/qUaQmI)
