title: deprecated after_save solution in rails 3
body: <p>hi 
          I am create one application in rails 3 I am using paperclip in which i want to invoke one paperclip function for generate a thumbnail of image but when I invoke a after_save method it will give a error </p>
  
  <p><strong>DEPRECATION WARNING: Base#after_save has been deprecated, please use Base.after_save :method instead. (called from  at app/models/asset.rb:23)</strong></p>