In _DummyThread objects the lock stored in __block (allocated thanks to
_Thread.__init__) was never used.  This is a waste since locks use OS
primitives that are in limited supply.  So the lock is deleted in
_DummyThread.__init__ .

Closes bug #1089632.
diff --git a/Misc/NEWS b/Misc/NEWS
index d7b35d5..8d00f22 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -33,6 +33,11 @@
 Library
 -------
 
+- _DummyThread objects in the threading module now delete self.__block that is
+  inherited from _Thread since it uses up a lock allocated by 'thread'.  The
+  lock primitives tend to be limited in number and thus should not be wasted on
+  a _DummyThread object.  Fixes bug #1089632.
+
 - The imghdr module now detects Exif files.
 
 - StringIO.truncate() now correctly adjusts the size attribute.