Using unittest2 in place of unittest

Used for Python 2.6 compatibility in testing.
diff --git a/tests/test_http.py b/tests/test_http.py
index c0ec5f9..a3ff0ac 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -27,7 +27,7 @@
 import httplib2
 import logging
 import os
-import unittest
+import unittest2 as unittest
 import urllib
 import random
 import StringIO