add wiki diff

app/views/wiki_page_versions/diff.html.erb

@@ -0,0 +1,13 @@
+<div id="c-wiki-pages">
+  <div id="a-diff">
+    <h1>Wiki Page: <%= @thispage.title %></h1>
+
+    <p>Showing differences between <%= compact_time @thispage.created_at %> (<%= link_to @thispage.updater.name, user_path(@thispage.updater) %>) and <%= compact_time @otherpage.created_at %> (<%= link_to @otherpage.updater.name, user_path(@otherpage.updater) %>)</p>
+
+    <div>
+      <%= wiki_page_diff(@thispage, @otherpage) %>
+    </div>
+  </div>
+</div>
+
+<%= render "wiki_pages/secondary_links" %>