Fixed images popup in autoloaded posts.

boards/templates/boards/post.html

@@ -13,7 +13,7 b''
                 class="thumb"
                 href="{{ post.image.url }}"><img
                 src="{{ post.image.url_200x150 }}"
-                alt="{% trans 'Post image' %}"
+                alt="{{ post.id }}"
                 data-width="{{ post.image_width }}"
                 data-height="{{ post.image_height }}"/>
         </a>