Add a deprecation message to activerecord.errors.

activerecord/lib/active_record/railtie.rb

@@ -67,5 +67,16 @@ class Railtie < Rails::Railtie
       end
     end
 
+    initializer "active_record.i18n_deprecation" do
+      require 'active_support/i18n'
+
+      begin
+        I18n.t(:"activerecord.errors", :raise => true)
+        warn "[DEPRECATION] \"activerecord.errors\" namespace is deprecated in I18n " << 
+          "yml files, please use just \"errors\" instead."
+      rescue Exception => e
+        # No message then.
+      end
+    end
   end
 end