Fix Django 1.7 compatibility
Created originally on Bitbucket by Anonymous
Was already merged in Bitbucket before import, marked as merged by the import user
django.contrib.auth.hashers is not a good idea as it is implementation specific and breaks with Django 1.7 which no longer imports
SortedDict. By directly importing those from
django.utils.datastructures the code works and should be backwards compatible with all Django versions currently targeted by passlib.