Update to current rust: use the new attributes syntax.
Update to current rust: libc is in its own crate.
Update to current rust: change the syntax for closure fields.
Update to current rust: struct fields are private by default.

Builds with mozilla/rust@e263ef1df7b892ed29e53313565eb05ab75e52f4.
Merge pull request #18 from mozilla-servo/rustup_20140410

Update to current rust