Fixed warnings if Python is run with -3.

This also adds proper hashing and comparision support to
undefined objects.

This fixes #224
diff --git a/CHANGES b/CHANGES
index 1c7caf4..01afc4e 100644
--- a/CHANGES
+++ b/CHANGES
@@ -10,6 +10,9 @@
 - Fixed lack of Python 3 support for bytecode caches.
 - Reverted support for defining blocks in included templates as this
   broke existing templates for users.
+- Fixed some warnings with hashing of undefineds and nodes if Python
+  is run with warnings for Python 3.
+- Added support for properly hashing undefined objects.
 
 Version 2.7
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