Edit post as anonymous user

[vincentporte]

Hi @ellmetha,
Using anonymous user capabilities, we found that editing a post a anonymous user made, by him.her.self fails.

Error Message : Cannot assign "<SimpleLazyObject: <django.contrib.auth.models.AnonymousUser object at 0x7fa3c8230f10>>": "Post.updated_by" must be a "User" instance.

We embeded fix in our app, but it may be useful for everyone.
Class PostForm, method update_post

[vincentporte]

Fix and tests are ready in a local new branch of your repo. Let me know if you're interested in me creating a PR.

[vincentporte]

Hi, I catched the same error when editing Topic as anonymous user. Let's keep in touch if I can help.