Restore compatibility with Python 2.6

Needed to work on XO with Fedora 11 / Python 2.6 - as still found on the field in Peru.

https://github.com/icarito/peru-learns-english/commit/87e82040705ee50b6e37f999b29ea2dbc990d1c8
Merge pull request #74 from icarito/patch-2

Restore compatibility with Python 2.6