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

Importing _ and SortedDict from 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.translation and django.utils.datastructures the code works and should be backwards compatible with all Django versions currently targeted by passlib.