Fix topic merge

It was merging in the wrong direction, and didn't update response count.

app/controllers/forum_topics_controller.rb

@@ -78,7 +78,7 @@ class ForumTopicsController < ApplicationController
     @forum_topic = ForumTopic.find(params[:id])
     @merged_topic = ForumTopic.find(params[:merged_id])
     @forum_topic.merge(@merged_topic)
-    redirect_to forum_topic_path(@forum_topic)
+    redirect_to forum_topic_path(@merged_topic)
   end
 
 private

app/models/forum_topic.rb

@@ -151,7 +151,8 @@ class ForumTopic < ActiveRecord::Base
   end
 
   def merge(topic)
-    ForumPost.where(:id => topic.posts.map(&:id)).update_all(:topic_id => id)
-    update_attribute(:is_deleted, true)
+    ForumPost.where(:id => self.posts.map(&:id)).update_all(:topic_id => topic.id)
+    topic.update_attribute(:response_count, topic.response_count + self.posts.length)
+    self.update_columns(:response_count => 0, :is_deleted => true)
   end
 end