validate author of trip on editing

templates/logbookform.html

@@ -36,13 +36,15 @@
            required /> 
            </span>
           
-    <br /><br />       
+    <br /><br />     
+           <span {% if authorflag %}style="color:red"{% endif %}>    
            <label for="author">Your name (author) <a href="/aliases/{{year}}">[valid authors]</a></label>
            <input {% if not user.username %} disabled{% endif %} 
            label = "author" name = "author" size="20"
            title="The person writing the logbook entry"
            {% if author %}value="{{author}}"{% else %}placeholder="Animal"{% endif %}
            required /> 
+          </span>
     <br /><br />        
            <label for="others">Other names (comma separated) <a href="/aliases/{{year}}">[valid aliases]</a></label>
            <input {% if not user.username %} disabled{% endif %}