Macros inside default methods throw internal compiler error

Using a macro from within a trait's default method causes an internal compiler error:

``` rust
trait Foo {
  fn val() -> int;
  fn print() {
    io::println(fmt!("%?", self.val()));
  }
}

struct Bar { 
  val: int,
}

impl Bar: Foo {
  fn val() -> int { self.val }
 }
```

error: internal compiler error: unexpanded macro
