Make task.rs export local_data. This is a hack to work around #2945.

Author: msullivan

src/libcore/task.rs

@@ -72,6 +72,10 @@ export thread_per_task;
 export manual_threads;
 export osmain;
 
+// FIXME (See #2945): This shouldn't be exported, but is to work around
+// what appears to be a metadata bug.
+export local_data;
+
 /* Data types */
 
 /// A handle to a task