std: Stabilize unit, bool, ty, tuple, arc, any

This commit applies stability attributes to the contents of these modules,
summarized here:

* The `unit` and `bool` modules have become #[unstable] as they are purely meant
  for documentation purposes and are candidates for removal.

* The `ty` module has been deprecated, and the inner `Unsafe` type has been
  renamed to `UnsafeCell` and moved to the `cell` module. The `marker1` field
  has been removed as the compiler now always infers `UnsafeCell` to be
  invariant. The `new` method i stable, but the `value` field, `get` and
  `unwrap` methods are all unstable.

* The `tuple` module has its name as stable, the naming of the `TupleN` traits
  as stable while the methods are all #[unstable]. The other impls in the module
  have appropriate stability for the corresponding trait.

* The `arc` module has received the exact same treatment as the `rc` module
  previously did.

* The `any` module has its name as stable. The `Any` trait is also stable, with
  a new private supertrait which now contains the `get_type_id` method. This is
  to make the method a private implementation detail rather than a public-facing
  detail.

  The two extension traits in the module are marked #[unstable] as they will not
  be necessary with DST. The `is` method is #[stable], the as_{mut,ref} methods
  have been renamed to downcast_{mut,ref} and are #[unstable].

  The extension trait `BoxAny` has been clarified as to why it is unstable as it
  will not be necessary with DST.

This is a breaking change because the `marker1` field was removed from the
`UnsafeCell` type. To deal with this change, you can simply delete the field and
only specify the value of the `data` field in static initializers.

[breaking-change]

1 files changed, 4 insertions, 1 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 89f6e934ad2..58278d5664e 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -87,10 +87,12 @@ impl<T: Ord> Ord for Box<T> {
 impl<T: Eq> Eq for Box<T> {}
 
 /// Extension methods for an owning `Any` trait object
-#[unstable = "post-DST, the signature of `downcast` will change to take `Box<Self>`"]
+#[unstable = "post-DST and coherence changes, this will not be a trait but \
+              rather a direct `impl` on `Box<Any>`"]
 pub trait BoxAny {
     /// Returns the boxed value if it is of type `T`, or
     /// `Err(Self)` if it isn't.
+    #[unstable = "naming conventions around accessing innards may change"]
     fn downcast<T: 'static>(self) -> Result<Box<T>, Self>;
 
     /// Deprecated; this method has been renamed to `downcast`.
@@ -100,6 +102,7 @@ pub trait BoxAny {
     }
 }
 
+#[stable]
 impl BoxAny for Box<Any> {
     #[inline]
     fn downcast<T: 'static>(self) -> Result<Box<T>, Box<Any>> {