Add proper disqus identifier comment count links

Fixes #277

.themes/classic/source/_includes/article.html

@@ -9,7 +9,8 @@
       <p class="meta">
         {% include post/date.html %}{{ time }}
         {% if site.disqus_short_name and page.comments != false and post.comments != false and site.disqus_show_comment_count == true %}
-         | <a href="{% if index %}{{ root_url }}{{ post.url }}{% endif %}#disqus_thread">Comments</a>
+           | <a href="{% if index %}{{ root_url }}{{ post.url }}{% endif %}#disqus_thread"
+             data-disqus-identifier="{% if post.meta.disqus_id %}{{ post.meta.disqus_id }}{% else %}{{ site.url }}{{ post.url }}{% endif %}">Comments</a>
         {% endif %}
       </p>
     {% endunless %}