FIX: Fix html response in development after ApplicationController reload

In development, if the ApplicationController is reloaded, then, previous
to this commit we were emitting an instance of the previous RenderEmpty
class, but rescuing from the reloaded instance.

Looking up RenderEmpty by its fully qualified name fixes this.

app/controllers/application_controller.rb

@@ -650,7 +650,7 @@ class ApplicationController < ActionController::Base
   def check_xhr
     # bypass xhr check on PUT / POST / DELETE provided api key is there, otherwise calling api is annoying
     return if !request.get? && (is_api? || is_user_api?)
-    raise RenderEmpty.new unless ((request.format && request.format.json?) || request.xhr?)
+    raise ApplicationController::RenderEmpty.new unless ((request.format && request.format.json?) || request.xhr?)
   end
 
   def self.requires_login(arg = {})