std: Modernize the local_data api

This commit brings the local_data api up to modern rust standards with a few key
improvements:

* The `pop` and `set` methods have been combined into one method, `replace`

* The `get_mut` method has been removed. All interior mutability should be done
  through `RefCell`.

* All functionality is now exposed as a method on the keys themselves. Instead
  of importing std::local_data, you now use "key.replace()" and "key.get()".

* All closures have been removed in favor of RAII functionality. This means that
  get() and get_mut() no long require closures, but rather return
  Option<SmartPointer> where the smart pointer takes care of relinquishing the
  borrow and also implements the necessary Deref traits

* The modify() function was removed to cut the local_data interface down to its
  bare essentials (similarly to how RefCell removed set/get).

[breaking-change]

src/test/auxiliary/macro_crate_outlive_expansion_phase.rs

@@ -15,7 +15,6 @@
 extern crate syntax;
 
 use std::any::Any;
-use std::local_data;
 use syntax::ast::Name;
 use syntax::ext::base::SyntaxExtension;
 
@@ -30,6 +29,6 @@ impl Drop for Foo {
 #[macro_registrar]
 pub fn registrar(_: |Name, SyntaxExtension|) {
     local_data_key!(foo: Box<Any:Send>);
-    local_data::set(foo, box Foo { foo: 10 } as Box<Any:Send>);
+    foo.replace(Some(box Foo { foo: 10 } as Box<Any:Send>));
 }
 

src/test/compile-fail/core-tls-store-pointer.rs

@@ -10,8 +10,6 @@
 
 // Testing that we can't store a reference it task-local storage
 
-use std::local_data;
-
 local_data_key!(key: @&int)
 //~^ ERROR missing lifetime specifier
 

src/test/compile-fail/macro-local-data-key-priv.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::local_data;
-
 // check that the local data keys are private by default.
 
 mod bar {
@@ -17,6 +15,6 @@ mod bar {
 }
 
 fn main() {
-    local_data::set(bar::baz, -10.0);
+    bar::baz.replace(Some(-10.0));
     //~^ ERROR static `baz` is private
 }

src/test/run-pass/macro-local-data-key.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::local_data;
-
 local_data_key!(foo: int)
 
 mod bar {
@@ -17,12 +15,12 @@ mod bar {
 }
 
 pub fn main() {
-    local_data::get(foo, |x| assert!(x.is_none()));
-    local_data::get(bar::baz, |y| assert!(y.is_none()));
+    assert!(foo.get().is_none());
+    assert!(bar::baz.get().is_none());
 
-    local_data::set(foo, 3);
-    local_data::set(bar::baz, -10.0);
+    foo.replace(Some(3));
+    bar::baz.replace(Some(-10.0));
 
-    local_data::get(foo, |x| assert_eq!(*x.unwrap(), 3));
-    local_data::get(bar::baz, |y| assert_eq!(*y.unwrap(), -10.0));
+    assert_eq!(*foo.get().unwrap(), 3);
+    assert_eq!(*bar::baz.get().unwrap(), -10.0);
 }