Standardize links to wiki help pages.

* Fix inconsistencies in how wiki pages were linked.

* Link directly to the wiki instead of to a title search that is expected
  to redirect to the wiki.

app/views/posts/show.html.erb

@@ -113,7 +113,7 @@
 
   <section id="comments">
     <% if !CurrentUser.user.is_builder? %>
-      <h2>Before commenting, read the <%= link_to "how to comment guide", wiki_pages_path(:search => {:title => "howto:comment"}) %>.</h2>
+      <h2>Before commenting, read the <%= link_to_wiki "how to comment guide", "howto:comment" %>.</h2>
     <% end %>
     <%= render "comments/partials/index/list", comments: @comments, post: @post, page: :post %>
   </section>