Python 3 compat.

Try to keep our Python sources compatible with both Python 2.7 and 3.

Check with 'pylint --py3k' and 'python -3'.

meta/constant_hash.py

@@ -5,6 +5,7 @@ The `constant_hash` module can generate constant pre-populated hash tables. We
 don't attempt parfect hashing, but simply generate an open addressed
 quadratically probed hash table.
 """
+from __future__ import absolute_import
 
 
 def simple_hash(s):