Change the way nuked users' posts are handled. Allow null in the user_id column of posts. Show these posts in the posts stream.

db/migrate/20130903154323_allow_null_user_id_on_posts.rb

@@ -0,0 +1,12 @@
+class AllowNullUserIdOnPosts < ActiveRecord::Migration
+  def up
+    change_column :posts, :user_id, :integer, null: true
+    execute "UPDATE posts SET user_id = NULL WHERE nuked_user = true"
+    remove_column :posts, :nuked_user
+  end
+
+  def down
+    add_column    :posts, :nuked_user, :boolean, default: false
+    change_column :posts, :user_id, :integer, null: false
+  end
+end