Fix friendly finds on Rails 4.2

Rails has done its usual song and dance and changed the way Model.find
works in 4.2, so it's now no longer delegated to the internal relation
class, but is its own method, so we solve this by including the finders
module in the model class as well as the relation class.

Resolves #607

lib/friendly_id/finders.rb

@@ -76,6 +76,9 @@ def relation_delegate_class(klass)
     def self.setup(model_class)
       model_class.instance_eval do
         relation.class.send(:include, friendly_id_config.finder_methods)
+        if ActiveRecord::VERSION::MAJOR == 4 && ActiveRecord::VERSION::MINOR == 2
+          model_class.send(:extend, friendly_id_config.finder_methods)
+        end
       end
     end
 

lib/friendly_id/history.rb

@@ -60,6 +60,9 @@ def self.setup(model_class)
         friendly_id_config.finder_methods = FriendlyId::History::FinderMethods
         if friendly_id_config.uses? :finders
           relation.class.send(:include, friendly_id_config.finder_methods)
+          if ActiveRecord::VERSION::MAJOR == 4 && ActiveRecord::VERSION::MINOR == 2
+            model_class.send(:extend, friendly_id_config.finder_methods)
+          end
         end
       end
     end