Use CanCanCan for messages controller

app/abilities/ability.rb

@@ -17,6 +17,7 @@ class Ability
     if user
       can :welcome, :site
       can [:create, :edit, :comment, :subscribe, :unsubscribe], DiaryEntry
+      can [:new, :create, :reply, :show, :inbox, :outbox, :mark, :destroy], Message
       can [:close, :reopen], Note
       can [:new, :create], Report
       can [:account, :go_public, :make_friend, :remove_friend, :api_details, :api_gpx_files], User

app/controllers/messages_controller.rb

@@ -3,7 +3,9 @@ class MessagesController < ApplicationController
 
   before_action :authorize_web
   before_action :set_locale
-  before_action :require_user
+
+  authorize_resource
+
   before_action :lookup_user, :only => [:new, :create]
   before_action :check_database_readable
   before_action :check_database_writable, :only => [:new, :create, :reply, :mark, :destroy]