TST: Import super from builtins.

Done to not break the build in python 2, see http://odl.readthedocs.org/guide/faq.html#errors-related-to-python-2-3. Issues #49 and #73.

test/operator/operator_utilities_test.py

@@ -20,6 +20,7 @@
 from __future__ import print_function, division, absolute_import
 from future import standard_library
 standard_library.install_aliases()
+from builtins import super
 
 # External module imports
 import pytest