title: popular flame icon does not display in CKAN
body: <p><strong>Scenario:</strong></p>
  
  <p>I'm using default popular function in helpers.py. However, it will not display the icon after a package/resource which has more than 10 views. How I set the popular function in my <code>resource_item.html</code> template is as follow:</p>
  
  <pre><code>{{ h.popular('views', res.tracking_summary.total, min=10) }}
  </code></pre>
  
  <p>I've also checked out the snippet which will be rendered by <code>h.popular</code>:</p>
  
  <pre><code>{% if number &gt;= min %}
  &lt;span class="popular ckan-icon ckan-icon-flame" title="{{ title.format(number=number) }}" xmlns="http://www.w3.org/1999/xhtml"&gt;{{ _('Popular') }}&lt;/span&gt;
  {% endif %}
  </code></pre>
  
  <p>It can only render the text 'Popular'. I tried to remove the text, and it seems like CKAN can not get the <code>ckan-icon-flame</code>. Then I checked <code>icons.less</code>, and <code>ckan-icon-flame</code> has been defined.</p>
  
  <p><strong>Additional Information:</strong></p>
  
  <p>I implemented a customized tracking tool. So I didn't enable the <code>ckan.tracking_enabled</code> in my <code>ckan.ini</code> file. I wonder if this change is related to load the icon correctly. But based on my readings of the code, I didn't find there's any condition related to the render of icon.</p>
  
  <p><strong>More Information:</strong></p>
  
  <p>variable.less:</p>
  
  <pre><code>@imagePath: "../../../base/images";
  @spritePath: "@{imagePath}/sprite-ckan-icons.png";
  </code></pre>
  
  <p>icons.less:</p>
  
  <pre><code>.ckan-icon {
      //.ie7-restore-right-whitespace;
      display: inline-block;
      vertical-align: text-bottom;
      position: relative;
      top: 2px;
      width: 16px;
      height: 16px;
      background-image: url("@{imagePath}/sprite-ckan-icons.png");
      background-repeat: no-repeat;
      background-position: 16px 16px;
  }
  
  .ckan-icon-background-position(@offset,
  @size) {
      @w: "@{size}X";
      @h: "@{size}Y";
      @x: "@{size}OffsetX";
      @y: "@{size}OffsetY";
      width: @@w;
      height: @@h;
      background-position: (@@x * @offset) @@y;
  }
  
  .ckan-icon-flame {
      .ckan-icon-background-position(2,
      "medium")
  }
  </code></pre>