Fix error_messages_for when instance variable names are given.

Signed-off-by: Joshua Peek <josh@joshpeek.com>

actionpack/lib/action_view/helpers/active_model_helper.rb

@@ -191,13 +191,13 @@ def error_messages_for(*params)
         options = params.extract_options!.symbolize_keys
 
         objects = Array.wrap(options.delete(:object) || params).map do |object|
-          unless object.respond_to?(:to_model)
-            object = instance_variable_get("@#{object}")
-            object = convert_to_model(object)
-          else
-            object = object.to_model
-            options[:object_name] ||= object.class.model_name.human
+          object = instance_variable_get("@#{object}") unless object.respond_to?(:to_model)
+          object = convert_to_model(object)
+
+          if object.class.respond_to?(:model_name)
+            options[:object_name] ||= object.class.model_name.human.downcase
           end
+
           object
         end
 

activemodel/lib/active_model/translation.rb

@@ -45,6 +45,9 @@ class Name < String
     # it will underscore then humanize the class name (BlogPost.human_name #=> "Blog post").
     # Specify +options+ with additional translating options.
     def human(options={})
+      return @human unless @klass.respond_to?(:lookup_ancestors) &&
+                           @klass.respond_to?(:i18n_scope)
+
       defaults = @klass.lookup_ancestors.map do |klass|
         klass.model_name.underscore.to_sym
       end