Factor out <ins>/<del> css from #c-post-versions to .diff-list.

app/helpers/post_versions_helper.rb

@@ -1,7 +1,8 @@
 module PostVersionsHelper
   def post_version_diff(post_version)
     diff = post_version.diff(post_version.previous)
-    html = []
+    html = '<span class="diff-list">'
+
     diff[:added_tags].each do |tag|
       prefix = diff[:obsolete_added_tags].include?(tag) ? '+<ins class="obsolete">' : '<ins>+'
       html << prefix + link_to(wordbreakify(tag), posts_path(:tags => tag)) + '</ins>'
@@ -13,6 +14,8 @@ module PostVersionsHelper
     diff[:unchanged_tags].each do |tag|
       html << '<span>' + link_to(wordbreakify(tag), posts_path(:tags => tag)) + '</span>'
     end
-    return html.join(" ").html_safe
+
+    html << "</span>"
+    html.html_safe
   end
 end