Check for method_missing in public and protected

Ruby 2.0 changed the behavior of `respond_to?` without argument to
return only search for public method. We actually want to perform the
action only if `method_missing` is either in public or protected.

actionpack/lib/action_controller/metal/compatibility.rb

@@ -58,7 +58,8 @@ def _handle_method_missing
     end
 
     def method_for_action(action_name)
-      super || (respond_to?(:method_missing) && "_handle_method_missing")
+      super || ((self.class.public_method_defined?(:method_missing) ||
+        self.class.protected_method_defined?(:method_missing)) && "_handle_method_missing")
     end
   end
 end