fix update_session_auth_hash for django <1.7
fix update_session_auth_hash for django <1.7

kdzch/django-rest-auth,aexeagmbh/django-rest-auth,Tivix/django-rest-auth,philippeluickx/django-rest-auth,caruccio/django-rest-auth,maxim-kht/django-rest-auth,maxim-kht/django-rest-auth,caruccio/django-rest-auth