- 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/ACKS b/Misc/ACKS
index 51aff58..67d4040 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -123,6 +123,7 @@
 Andrew Dalke
 Lars Damerow
 Eric Daniel
+Scott David Daniels
 Ben Darnell
 Jonathan Dasteel
 John DeGood