[1.5.x] Updated the bundled version of six to 1.4.0.
[1.5.x] Updated the bundled version of six to 1.4.0.

Backport of 4292097078279226cb725c2921011fb14634b9af from master.

bliti/django-nonrel-1.5,ccn-2m/django,bliti/django-nonrel-1.5,ccn-2m/django,ccn-2m/django,ccn-2m/django,bliti/django-nonrel-1.5