Allow static variables in range expressions

``` rust
static foo: int = 16;

fn main() {
    match 15 {
        3 .. foo => io::println(~"success"),
        _ => fail!()
    }
}
```

```
/tmp/rusttest.rs:5:13: 5:16 error: unexpected token: `foo`
/tmp/rusttest.rs:5         3 .. foo => io::println(~"success"),
                                ^~~
```
