Applied Ulrich Kunitz's patches to slightly optimize Python serialization code.

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 4738f51..0772fd6 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -36,3 +36,5 @@
 
 Non-Google patch contributors:
   Kevin Ko <kevin.s.ko@gmail.com>
+  Johan Euphrosine <proppy@aminche.com>
+  Ulrich Kunitz <kune@deine-taler.de>