Merge pull request #4283 from lest/fix-singleton-checking

use correct variant of checking whether class is a singleton

activesupport/lib/active_support/core_ext/class/attribute.rb

@@ -110,6 +110,6 @@ class Class
 
   private
   def singleton_class?
-    !name || '' == name
+    ancestors.first != self
   end
 end