Make latest post redirect if the blog post redirects (alshedivat#1451)

Fixes alshedivat#1450, and the behavior of the site with this "new" code is shown
in the Expected behavior screenshots there.

I copy-pasted the redirect logic from `blog/index.html` into
`_includes/latest_posts.html`, with minor name changes.

I also cleaned up a line in `blog/index.html`.

Author: jesse-wei

_includes/latest_posts.html

@@ -14,7 +14,16 @@
                 <tr>
                   <th scope="row">{{ item.date | date: "%b %-d, %Y" }}</th>
                   <td>
-                    <a class="news-title" href="{{ item.url | relative_url }}">{{ item.title }}</a>
+                    {% if item.redirect == blank %}
+                      <a class="news-title" href="{{ item.url | relative_url }}">{{ item.title }}</a>
+                    {% elsif item.redirect contains '://' %}
+                      <a class="news-title" href="{{ item.redirect }}" target="_blank">{{ item.title }}</a>
+                      <svg width="2rem" height="2rem" viewBox="0 0 40 40" xmlns="http://www.w3.org/2000/svg">
+                        <path d="M17 13.5v6H5v-12h6m3-3h6v6m0-6-9 9" class="icon_svg-stroke" stroke="#999" stroke-width="1.5" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path>
+                      </svg>
+                    {% else %}
+                      <a class="news-title" href="{{ item.redirect | relative_url }}">{{ item.title }}</a>
+                    {% endif %}
                   </td>
                 </tr>
               {%- endfor %}

blog/index.html

@@ -59,16 +59,14 @@ <h2>{{ site.blog_description }}</h2>
 {%- endif -%}
         <h3>
         {% if post.redirect == blank %}
-          <a class="post-title" href="{{ post.url | prepend: site.baseurl }}">{{ post.title }}</a>
+          <a class="post-title" href="{{ post.url | relative_url }}">{{ post.title }}</a>
+        {% elsif post.redirect contains '://' %}
+          <a class="post-title" href="{{ post.redirect }}" target="_blank">{{ post.title }}</a>
+          <svg width="2rem" height="2rem" viewBox="0 0 40 40" xmlns="http://www.w3.org/2000/svg">
+            <path d="M17 13.5v6H5v-12h6m3-3h6v6m0-6-9 9" class="icon_svg-stroke" stroke="#999" stroke-width="1.5" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path>
+          </svg>
         {% else %}
-          {% if post.redirect contains '://' %}
-            <a class="post-title" href="{{ post.redirect }}" target="_blank">{{ post.title }}</a>
-            <svg width="2rem" height="2rem" viewBox="0 0 40 40" xmlns="http://www.w3.org/2000/svg">
-              <path d="M17 13.5v6H5v-12h6m3-3h6v6m0-6-9 9" class="icon_svg-stroke" stroke="#999" stroke-width="1.5" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path>
-            </svg>
-          {% else %}
-            <a class="post-title" href="{{ post.redirect | relative_url }}">{{ post.title }}</a>
-          {% endif %}
+          <a class="post-title" href="{{ post.redirect | relative_url }}">{{ post.title }}</a>
         {% endif %}
       </h3>
       <p>{{ post.description }}</p>