Enable absolute imports.

See PEP 328[1] for details. This feature was introduced in Python 2.5 and
will become mandatory in Python 3.

[1]: http://www.python.org/dev/peps/pep-0328

(imported from commit 7444eeba8a08d5f91b94c7921848f2274979bd76)

zephyr/lib/cache_helpers.py

@@ -1,3 +1,5 @@
+from __future__ import absolute_import
+
 # This file needs to be different from cache.py because cache.py
 # cannot import anything from zephyr.models or we'd have an import
 # loop