add ThreadError to threading.__all__ (closes #12679)
diff --git a/Lib/threading.py b/Lib/threading.py
index 222e5d9..b663232 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -20,7 +20,7 @@
 
 __all__ = ['active_count', 'Condition', 'current_thread', 'enumerate', 'Event',
            'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Thread', 'Barrier',
-           'Timer', 'setprofile', 'settrace', 'local', 'stack_size']
+           'Timer', 'ThreadError', 'setprofile', 'settrace', 'local', 'stack_size']
 
 # Rename some stuff so "from threading import *" is safe
 _start_new_thread = _thread.start_new_thread