show description diffs in pool version listing

app/helpers/pool_versions_helper.rb

@@ -12,6 +12,11 @@ module PoolVersionsHelper
       '<del><a href="/posts/' + post_id.to_s + '">' + post_id.to_s + '</a></del>'
     end.join(" ")
 
+    if pool_version.description_changed?
+      html << '<ins>desc:' + h(pool_version.description) + '</ins> '
+      html << '<del>desc:' + h(pool_version.previous.description) + '</del> '
+    end
+
     return html.html_safe
   end
 end

app/models/pool_archive.rb

@@ -59,6 +59,10 @@ class PoolArchive < ActiveRecord::Base
     sqs_service.send_message(msg)
   end
 
+  def previous
+    PoolArchive.where("pool_id = ? and version < ?", pool_id, version).order("version desc").first
+  end
+
   def pool
     Pool.find(pool_id)
   end