std: Second pass stabilization for thread_local

This commit performs a second pass over the `std::thread_local` module. Most of
the functionality remains explicitly unstable, but the specific actions taken
were:

* `thread_local` is now stable
* `thread_local!` is now stable
* `thread_local::Key` is now stable
* `thread_local::Key::with` is now stable
* `thread_local::Key::destroyed` is deprecated in favor of a more general
  `state` function
* `thread_local::Key::state` was added to query the three states that a key can
  be in: uninitialized, valid, or destroyed. This function, and the
  corresponding `State` enum, are both marked unstable as we may wish to expand
  it later on.
* `thread_local::scoped` is entirely unstable. There hasn't been a whole lot of
  usage of this module in the standard distribution, so it remains unstable at
  this time.

Note that while the structure `Key` is marked stable, it is currently forced to
expose all of its implementation details due to the use of
construction-via-macro. The use of construction-via-macro is currently required
in order to place the `#[thread_local]` attribute on static in a
platform-specific manner. These stability attributes were assigned assuming that
it will be acceptable to tweak the implementation of `Key` in the future.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/libstd/sys/common/thread_info.rs b/src/libstd/sys/common/thread_info.rs
index dc21feb17a8..b8bff23d583 100644
--- a/src/libstd/sys/common/thread_info.rs
+++ b/src/libstd/sys/common/thread_info.rs
@@ -10,9 +10,10 @@
 
 use core::prelude::*;
 
-use thread::Thread;
 use cell::RefCell;
 use string::String;
+use thread::Thread;
+use thread_local::State;
 
 struct ThreadInfo {
     // This field holds the known bounds of the stack in (lo, hi)
@@ -27,7 +28,7 @@ thread_local! { static THREAD_INFO: RefCell<Option<ThreadInfo>> = RefCell::new(N
 
 impl ThreadInfo {
     fn with<R>(f: |&mut ThreadInfo| -> R) -> R {
-        if THREAD_INFO.destroyed() {
+        if THREAD_INFO.state() == State::Destroyed {
             panic!("Use of std::thread::Thread::current() is not possible after \
                     the thread's local data has been destroyed");
         }