core: Move atomic into a new sync module

This mirrors the same hierarchy in the standard library.

src/liballoc/arc.rs

@@ -71,8 +71,8 @@
 
 use boxed::Box;
 
-use core::atomic;
+use core::sync::atomic;
-use core::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst};
+use core::sync::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst};
 use core::fmt;
 use core::cmp::Ordering;
 use core::mem::{align_of_val, size_of_val};

src/libcore/lib.rs

@@ -142,7 +142,7 @@ pub mod convert;
 
 pub mod any;
 pub mod array;
-pub mod atomic;
+pub mod sync;
 pub mod cell;
 pub mod char;
 pub mod panicking;

src/libcore/sync/mod.rs

@@ -0,0 +1,15 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Synchronization primitives
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+pub mod atomic;

src/libstd/sync/mod.rs

@@ -18,7 +18,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 pub use alloc::arc::{Arc, Weak};
-pub use core::atomic;
+pub use core::sync::atomic;
 
 pub use self::barrier::{Barrier, BarrierWaitResult};
 pub use self::condvar::{Condvar, StaticCondvar, CONDVAR_INIT};