title: Django sorl-thumbnail does not display images
body: <p>I try to use Django sorl-thumbnail but it does not display images (and does't show any errors).</p>
  
  <p>Settings.py:</p>
  
  <pre><code>INSTALLED_APPS = (
      ....
      'sorl.thumbnail',
  )
  </code></pre>
  
  <p>Models:</p>
  
  <pre><code>class Toy(models.Model):
      name = models.CharField(max_length=50, verbose_name=u'Name')
      image = ImageField(upload_to='site_media/images')
  </code></pre>
  
  <p>templates:</p>
  
  <pre><code>&lt;div id="toy"&gt;
                  {% for p in toys %}
                      &lt;div class="toy"&gt;
                                  # toy.image - this is model_name.image field
                              {% thumbnail toy.image "100x700" as im %}
                              &lt;img style="margin:{{ im|margin:"100x700" }}" src="{{ im.url }}" width="{{ im.x }}" height="{{ im.y }}"&gt;
                              {% endthumbnail %}
  
                              &lt;p&gt;
                              &lt;span&gt; {{ p.name }} &lt;/span&gt;
                              &lt;span&gt; {{p.unit_price}} &lt;/span&gt;
                              &lt;/p&gt;
                      &lt;/div&gt;
                  {% endfor %}
              &lt;/div&gt;
  </code></pre>
  
  <p>urls.py:</p>
  
  <pre><code>url(r'^site_media/(.*)$', 'django.views.static.serve', {'document_root' : os.path.join(os.path.dirname(__file__), 'site_media')}),
  </code></pre>