- Thanks to Scott David Daniels, a subtle bug in how the zlib
  extension implemented flush() was fixed.  Scott also rewrite the
  zlib test suite using the unittest module.  (SF bug #640230 and
  patch #678531.)

Backport candidate I think.
diff --git a/Misc/NEWS b/Misc/NEWS
index f1e0cd2..ece29b6 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -33,6 +33,11 @@
 Extension modules
 -----------------
 
+- Thanks to Scott David Daniels, a subtle bug in how the zlib
+  extension implemented flush() was fixed.  Scott also rewrite the
+  zlib test suite using the unittest module.  (SF bug #640230 and
+  patch #678531.)
+
 - Added an itertools module containing high speed, memory efficient
   looping constructs inspired by tools from Haskell and SML.