Fix warnings

Fixing unused attributes warnings required updating serde_macros
which required updating to rustc 1.6.0-nightly (a2866e387 2015-11-30)
which required updating some other dependencies.

components/compositing/scrolling.rs

@@ -7,7 +7,6 @@
 use compositor_task::{CompositorProxy, Msg};
 use std::sync::mpsc::{Receiver, Sender, channel};
 use std::thread::{self, Builder};
-use std::u32;
 use time;
 use util::time::duration_from_nanoseconds;