Replace migrations that rely on models with rake tasks

Replace some migrations that rely on relationships between
models to add subscriptions with rake tasks.

lib/tasks/subscribe_diary_authors.rb

@@ -0,0 +1,7 @@
+namespace :db do
+  task :subscribe_diary_authors => :environment do
+    DiaryEntry.find_each do |diary_entry|
+      diary_entry.subscriptions.create(:user => diary_entry.user) unless diary_entry.subscribers.exists?(diary_entry.user.id)
+    end
+  end
+end

lib/tasks/subscribe_old_changesets.rb

@@ -0,0 +1,7 @@
+namespace :db do
+  task :subscribe_old_changesets => :environment do
+    Changeset.find_each do |changeset|
+      changeset.subscribers << changeset.user unless changeset.subscribers.exists?(changeset.user.id)
+    end
+  end
+end