Subclass MiddlewareMixin for Django 1.10 compat

[jschneier]

Closes #953

[macolo]

@jschneier @omab is there a reason this PR cannot be merged?

It is very, very dear to me. :)

[omab]

@macolo, the reason is that I'm in the middle of migrating the project to http://github.com/python-social-auth, I need to port the PRs there first.

[jschneier]

@omab Can we at least merge this and then people can install from git? I think this is one of the last blockers for a lot of people to move to the new MIDDLEWARE setting in Django. I see the ongoing migration to the split repos but realistically for now it doesn't look like people are using that.

[omab]

@jschneier, sure, we can do it

[tdruez]

@jschneier thanks for the fix :)

@omab would you mind to issue a new release including this? Thanks!

[tdruez]

@omab sorry to insist, but is there anything blocking a Django 1.10 compatible package?

[omab]

@tdruez, I'm porting the app to https://github.com/python-social-auth, I suggest using the git reference in the requirements.txt to get this fix since I don't plan any release on python-social-auth until I fully port it to depend on the new packages.

[tdruez]

Alright, good luck with the migration!

[danni]

If you don't want to run the Git version, here's a workaround until this is released.

from django.utils.deprecation import MiddlewareMixin

import social.apps.django_app.middleware

class SocialAuthExceptionMiddleware(
        social.apps.django_app.middleware.SocialAuthExceptionMiddleware,
        MiddlewareMixin):
    """Work around Django 1.10 middleware incompatibility."""

    pass