Fix bug where a KeyError was raised if -O was being used for the interpreter
and Thread.__delete() was called after a Thread instance was created.  Problem
resulted from a currentThread() call in an 'assert' statement being optimized
out and dummy_thread.get_ident() always returning -1 and thus overwriting the
entry for the _MainThread() instance created in 'threading' at import time.

Closes bug #993394.
diff --git a/Misc/NEWS b/Misc/NEWS
index f679239..af7b384 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -39,6 +39,10 @@
 Library
 -------
 
+- Bug #993394.  Fix a possible red herring of KeyError in 'threading' being
+  raised during interpreter shutdown from a registered function with atexit
+  when dummy_threading is being used.
+
 - Bug #857297/Patch #916874.  Fix an error when extracting a hard link
   from a tarfile.