auto merge of #15591 : aturon/rust/box-cell-stability, r=alexcrichton

This PR is the outcome of the library stabilization meeting for the
`liballoc::owned` and `libcore::cell` modules.

Aside from the stability attributes, there are a few breaking changes:

* The `owned` modules is now named `boxed`, to better represent its
  contents. (`box` was unavailable, since it's a keyword.) This will
  help avoid the misconception that `Box` plays a special role wrt
  ownership.

* The `AnyOwnExt` extension trait is renamed to `BoxAny`, and its `move`
  method is renamed to `downcast`, in both cases to improve clarity.

* The recently-added `AnySendOwnExt` extension trait is removed; it was
  not being used and is unnecessary.

[breaking-change]

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libsync/mpsc_queue.rs b/src/libsync/mpsc_queue.rs
index ecd37e68880..759695fe5b6 100644
--- a/src/libsync/mpsc_queue.rs
+++ b/src/libsync/mpsc_queue.rs
@@ -42,7 +42,7 @@
 
 use core::prelude::*;
 
-use alloc::owned::Box;
+use alloc::boxed::Box;
 use core::mem;
 use core::ty::Unsafe;