revert unexpected change for py26

python/google/protobuf/internal/proto_builder_test.py

@@ -36,7 +36,10 @@ try:
     from collections import OrderedDict
 except ImportError:
     from ordereddict import OrderedDict  #PY26
-import unittest
+try:
+  import unittest2 as unittest
+except ImportError:
+  import unittest
 from google.protobuf import descriptor_pb2
 from google.protobuf import descriptor_pool
 from google.protobuf import proto_builder