ledermann/unread — pull request #38 by nazgum (2014-05-13 05:32:46+00:00)
Title: Fix unread_by scope to work with associations

In rails 4.1 Post.unread_by(user) works, but @site.posts.unread_by(user) does not,
as self refers to the association rather than the class, so read_mark_global is not found.

Using self.base_class fixes it up =)