Fix wording in LocalKey documentation

src/libstd/sync/once.rs

@@ -316,7 +316,7 @@ impl Once {
                         }
 
                         // Once we've enqueued ourselves, wait in a loop.
-                        // Aftewards reload the state and continue with what we
+                        // Afterwards reload the state and continue with what we
                         // were doing from before.
                         while !node.signaled.load(Ordering::SeqCst) {
                             thread::park();

src/libstd/thread/local.rs

@@ -28,8 +28,8 @@ use mem;
 /// # Initialization and Destruction
 ///
 /// Initialization is dynamically performed on the first call to `with()`
-/// within a thread, and values support destructors which will be run when a
-/// thread exits.
+/// within a thread, and values that implement `Drop` get destructed when a
+/// thread exits. Some caveats apply, which are explained below.
 ///
 /// # Examples
 ///