title: Extending ActsAsTaggableOn to have Images, but getting "Can't mass-assign protected attributes: tag_image" Error
body: <p>I'm using the <a href="https://github.com/mbleigh/acts-as-taggable-on" rel="nofollow">acts_as_taggable_on</a> gem to tag ads. It works fine, but I need the tags to have images, so I decided to extend the plugin and writed this module:</p>
  
  <pre><code># Add logic to ActsAsTaggableOn Tag model
  module TagExtend
  
    def self.included(recipient)
      recipient.extend(ClassMethods)
    end
    module ClassMethods
  
      ActiveRecord::Base.attr_accessible :tag_image
      ActiveRecord::Base.has_attached_file :tag_image,
        :styles =&gt; { :medium =&gt; "300x200&gt;"},
        :storage =&gt; :s3,
        :bucket =&gt; S3_BUCKET,   
        :s3_host_name =&gt;  S3_HOST,
        :s3_credentials =&gt; {
          :access_key_id =&gt; S3_KEY,
          :secret_access_key =&gt;S3_SECRET      
        }
    end
  
  end
  </code></pre>
  
  <p>And in an initializer file:</p>
  
  <pre><code>require File.dirname(__FILE__) + '/../../lib/tag_extend.rb'
  ActsAsTaggableOn::Tag.send(:include, TagExtend)
  </code></pre>
  
  <p>It should work, but when I try to save a Tag with an image (from ActiveAdmin) I'm getting: <code>Can't mass-assign protected attributes: tag_image</code></p>
  
  <p>Any suggestion on this ?</p>