Modernize the seed file and provide protection for when there is no U…

…ser model or when the User exists and already has the plugin added to their list somehow.

lib/generators/templates/db/seeds/image_rotators.rb

@@ -1,4 +1,8 @@
-User.find(:all).each do |user|
-  user.plugins.create(:name => "image_rotators",
-                      :position => (user.plugins.maximum(:position) || -1) +1)
+if defined?(::User)
+  User.find(:all).each do |user|
+    if user.plugins.where(:name => 'image_rotators').blank?
+      user.plugins.create(:name => "image_rotators",
+                          :position => (user.plugins.maximum(:position) || -1) +1)
+    end
+  end
 end