It might not be so simple. The docs indicate that this changed in 1.6, but since this is builtin stuff, it might not be possible to support both.
https://docs.djangoproject.com/en/dev/releases/1.6/#django-contrib-auth-password-reset-uses-base-64-encoding-of-user-pk

If that's the case, we should stick with 1.5 for now.