#1866: support gelbooru source redirection

doesn't support the discontinued sha1 naming scheme in some older files

app/models/post.rb

@@ -324,6 +324,9 @@ class Post < ActiveRecord::Base
       when %r{\Ahttp://static[1-6]?\.minitokyo\.net/(?:downloads|view)/(?:\d{2}/){2}(\d+)}i
         "http://gallery.minitokyo.net/download/#{$1}"
 
+      when %r{\Ahttp://(?:(?:s?img|cdn|www)\d?\.)?gelbooru\.com/{1,2}(?:images|samples)/\d+/(?:sample_)?([a-f0-9]{32})\.}i
+        "http://gelbooru.com/index.php?page=post&s=list&md5=#{$1}"
+  
       else
         source
       end