title: undefined method when using Sidekiq's delayed_extensions
body: <p>When using <a href="https://github.com/mperham/sidekiq/wiki/Delayed-Extensions" rel="nofollow">Sidekiq's delayed extensions</a>, I get this error in my <code>bundle exec sidekiq</code> shell:</p>
  
  <pre><code>2013-03-06T04:13:57Z 52099 TID-ouqzj4xl8 WARN: undefined method `send_message' for #&lt;Class:0x007f8a783d72f0&gt;
  </code></pre>
  
  <p><strong>In my controller:</strong></p>
  
  <pre><code>MyClass.delay_until(10.seconds.from_now, :retry =&gt; true).send_message(deliver_sms, phone)
  </code></pre>
  
  <p><strong>In my model:</strong></p>
  
  <pre><code>require 'sidekiq'
  
  class MyClass &lt; ActiveRecord::Base
  
    include Sidekiq::Extensions
  
    def self.send_message(deliver_sms, phone)
      message_id = deliver_sms.deliver(phone, 'This is a test message') 
    end
  end
  </code></pre>
  
  <p>Any help would be appreciated</p>