fixes #442

app/models/forum_post.rb

@@ -114,6 +114,10 @@ class ForumPost < ActiveRecord::Base
     "[quote]\n#{creator_name} said:\n\n#{stripped_body}\n[/quote]\n\n"
   end
   
+  def forum_topic_page
+    ((ForumPost.where("topic_id = ? and created_at < ?", topic_id, created_at).count + 1) / Danbooru.config.posts_per_page.to_f).ceil
+  end
+  
   def build_response
     dup.tap do |x|
       x.body = x.quoted_response