Avoid eagerly generating Module delegation methods

We special case singleton methods being added to ActiveRecord::Base
subclasses whose names match methods on Kernel so that we can eagerly
define them on the ClassSpecificRelation as otherwise we'd never hit
method_missing.

Previously, this would also eagerly define methods which were on the
Kernel Module's singleton class rather than being defined as instance
methods inside the module.

Most notably this hit "name" which is defined on the anonymous HABTM
classes.

Author: jhawthorn

activerecord/lib/active_record/scoping/named.rb

@@ -190,7 +190,10 @@ def scope(name, body, &block)
 
         private
           def singleton_method_added(name)
-            generate_relation_method(name) if Kernel.respond_to?(name) && !ActiveRecord::Relation.method_defined?(name)
+            # Most Kernel extends are both singleton and instance methods so
+            # respond_to is a fast check, but we don't want to define methods
+            # only on the module (ex. Module#name)
+            generate_relation_method(name) if Kernel.respond_to?(name) && (Kernel.instance_methods | Kernel.private_instance_methods).include?(name) && !ActiveRecord::Relation.method_defined?(name)
           end
       end
     end