Follow rustc 0.11-pre (a990920 2014-05-08)

- Remove all of ~ signs
- Wrap a closure in Data::Fun by RefCell
  - because a mutable reference of closure can be called, while an immutable ref can't.
Merge pull request #16 from Kroisse/follow

Follow rustc 0.11-pre (a990920 2014-05-08)