failed at 'assertion failed: prev >= 0', /Users/kevin/Dev/rust/rust/src/libstd/comm/stream.rs:355

I hit an assertion failure today:

```
failed at 'assertion failed: prev >= 0', /Users/kevin/Dev/rust/rust/src/libstd/comm/stream.rs:355
```

I believe what happened was I closed a Chan while the Port was being selected on.

@alexcrichton says he knows what's going on already.
