servo: Merge #8446 - Rust upgrade to rustc 1.6.0-nightly (5b4986fa5 2015-11-08) (from servo:rustup_20151110); r=SimonSapin+Ms2ger+jdm+Manishearth

<s>DO NOT r+ or try+ this</s>

<s>It causes an OOM (https://github.com/rust-lang/rust/issues/29740) and can crash the OS. Probably will set our CI on fire. </s>

Source-Repo: https://github.com/servo/servo
Source-Revision: f13c72d68e1e7f49e241938bfd6e8a588c68e86b

servo/components/util/workqueue.rs

@@ -8,7 +8,7 @@
 //! higher-level API on top of this could allow safe fork-join parallelism.
 
 use deque::{Abort, BufferPool, Data, Empty, Stealer, Worker};
-use libc::funcs::posix88::unistd::usleep;
+use libc::usleep;
 use rand::{Rng, XorShiftRng, weak_rng};
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::mpsc::{Receiver, Sender, channel};