put message template in separate file

bookshare/templates/messages.html

+{% if messages %}
+  {% for message in messages %}
+  <div class="row">
+    <div class="col-md-12">
+      <div class="alert alert-info alert-dismissable text-center" role="alert">
+      <button type="button" class="close" data-dismiss="alert" aria-label="close"><span aria-hidden="true">&times;</span></button>
+      <strong>{{ message }}</strong>
+      </div>
+    </div>
+  </div>
+  {% endfor %}
+{% endif %}

bookshare/trades/templates/detail_listing.html

@@ -44,18 +44,7 @@ SRCT Bookshare • {{ listing.title }}
 </div>
 {% endif %}
 
-{% if messages %}
-  {% for message in messages %}
-  <div class="row">
-    <div class="col-md-12">
-      <div class="alert alert-info alert-dismissable text-center" role="alert">
-      <button type="button" class="close" data-dismiss="alert" aria-label="close"><span aria-hidden="true">&times;</span></button>
-      <strong>{{ message }}</strong>
-      </div>
-    </div>
-  </div>
-  {% endfor %}
-{% endif %}
+{% include 'messages.html' %}
 
 {% if listing.cancelled %}
   <div class="row">