[PATCH][3.0] join doesn't work properly for association with :through

When you define an association like the following ...

class Author
   has_many :author
end
class Post
   belongs_to :author
end
class Comment
   belongs_to :post
   has_one :post_author, :through=>:post, :source=>:author
end

Then if you write the code like the following ...

comments = Comment.find :all, :conditions=>["authors.name = ?", "David"], :joins=>[:post_author]

You get a wrong SQL and result as you can see the test which is included in first commit of a patch uploading. The second commit of the patch fixes the issue.

This is a same issue as the following.
https://rails.lighthouseapp.com/projects/8994/tickets/3684-invalid-...

Since the patch is made against Rails 3 here, I create a new ticket.