Rename Share to Sync

This leaves the `Share` trait at `std::kinds` via a `#[deprecated]` `pub use`
statement, but the `NoShare` struct is no longer part of `std::kinds::marker`
due to #12660 (the build cannot bootstrap otherwise).

All code referencing the `Share` trait should now reference the `Sync` trait,
and all code referencing the `NoShare` type should now reference the `NoSync`
type. The functionality and meaning of this trait have not changed, only the
naming.

Closes #16281
[breaking-change]

src/libsyntax/ast.rs

@@ -208,7 +208,7 @@ pub static DUMMY_NODE_ID: NodeId = -1;
 /// The AST represents all type param bounds as types.
 /// typeck::collect::compute_bounds matches these against
 /// the "special" built-in traits (see middle::lang_items) and
-/// detects Copy, Send and Share.
+/// detects Copy, Send and Sync.
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)]
 pub enum TyParamBound {
     TraitTyParamBound(TraitRef),