Removed most of absolute_import imports

Should be unneeded with Python 2.7 and up.
Added some unicode_literals along the way.

tests/file_uploads/tests.py

@@ -1,5 +1,5 @@
 #! -*- coding: utf-8 -*-
-from __future__ import absolute_import, unicode_literals
+from __future__ import unicode_literals
 
 import base64
 import errno