Upgrade django to 1.6.5

The primary motivation for this upgrade is CVE-2014-0472
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-0472

"The django.core.urlresolvers.reverse function in Django before 1.4.11,
1.5.x before 1.5.6, 1.6.x before 1.6.3, and 1.7.x before 1.7 beta 2
allows remote attackers to import and execute arbitrary Python modules
by leveraging a view that constructs URLs using user input and a "dotted
Python path.""
Merge pull request #146 from alphagov/upgrade-django

Upgrade django to 1.6.5