fixes an edge bug discovered in multithreaded environments
bug explained here: http://code-trick.com/python-bug-attribute-error-_strptime/
python bug report: http://bugs.python.org/issue7980
attempt to fix travis build
Merge branch 'master' of https://github.com/mschettler/django-session-security into mschettler-master

Conflicts:
	session_security/utils.py