#1866: support e-shuushuu source redirection

* currently, e-shuushuu already redirects some posts to their landing pages (http://e-shuushuu.net/image/?image_id=$id), particularly those ending in 'jpg'
* for some reason, e-shuushuu doesn't natively support other formats even the uppercased 'JPG'
* the following lines aim to address this issue to redirect to http://e-shuushuu.net/image/$id
* http://e-shuushuu.net/image.php?mode=view&image_id=$id is also a valid alternative but is not used

app/models/post.rb

@@ -337,6 +337,9 @@ class Post < ActiveRecord::Base
         filename = $2
       "http://g.e-hentai.org/?f_shash=#{sha1hash}&fs_from=#{filename}"
       
+      when %r{\Ahttp://e-shuushuu.net/images/\d{4}-(?:\d{2}-){2}(\d+)}i
+      "http://e-shuushuu.net/image/#{$1}"
+
       else
         source
       end