ICE cannot relate bound region 

```
src/serial.rs:10:17: 10:26 error: internal compiler error: cannot relate bound region: ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(DefId { krate: 1, node: 61296 }, 'a)) <= '_#1r
src/serial.rs:10     for byte in s.bytes() {
                                 ^~~~~~~~~
```

``` rust
  pub fn puts(&self, s: &str) {
    for byte in s.bytes() {
      self.putc(byte)
    }
  }
```
