title: Carrierwave store_dir not modified when running rspec with spork
body: <p>I've followed the <a href="https://github.com/jnicklas/carrierwave/wiki/How-to%3A-Cleanup-after-your-Rspec-tests" rel="nofollow">instructions on how to define a test-specific store directory for carrierwave uploads</a>, which suggests opening the <code>CarrierWave::Uploader::Base</code> class and redefining <code>store_dir</code> and <code>cache_dir</code> like so:</p>
  
  <pre><code>if defined?(CarrierWave)
    CarrierWave::Uploader::Base.descendants.each do |klass|
      next if klass.anonymous?
      klass.class_eval do
        def cache_dir
          "#{Rails.root}/spec/support/uploads/tmp"
        end 
  
        def store_dir
          "#{Rails.root}/spec/support/uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
        end 
      end 
    end
  end
  </code></pre>
  
  <p>This works like a charm, except when I run rspec with spork, then it fails to modify the class and uploads are stored in the default location. Does anyone have any clue why this might be happening?</p>