title: Getting undefined method `contains_attachment?' when using sunspot_solr for search inside the documents/attachment
body: <p>I am trying to implement fulltext search inside attachments using sunspot_solr but getting <code>undefined method contains_attachment?</code> when running <code>rake sunspot:solr:reindex</code>.</p>
  
  <p>I am following this:
  <a href="https://cbpowell.wordpress.com/2012/09/18/indexing-rich-documents-with-rails-sunspot-solr-sunspot-cell-and-carrierwave-cookbook-style/" rel="nofollow noreferrer">https://cbpowell.wordpress.com/2012/09/18/indexing-rich-documents-with-rails-sunspot-solr-sunspot-cell-and-carrierwave-cookbook-style/</a></p>
  
  <p>Here's my Gemfile:</p>
  
  <pre><code>gem 'sunspot', :git =&gt; "git://github.com/sunspot/sunspot.git"
  gem 'sunspot_solr', :git =&gt; "git://github.com/sunspot/sunspot.git"
  gem 'sunspot_rails', :git =&gt; "git://github.com/sunspot/sunspot.git", :require =&gt; "sunspot_rails"
  gem 'sunspot_cell', :git =&gt; 'git://github.com/zheileman/sunspot_cell.git'
  gem 'sunspot_cell_jars'
  gem 'progress_bar'
  </code></pre>
  
  <p>Need help!!</p>