Fix #4178: add ability to mass undo tag edits.

Adds checkboxes to the /post_versions index allowing you to select and
undo multiple versions at once.

app/controllers/post_versions_controller.rb

@@ -2,8 +2,10 @@ class PostVersionsController < ApplicationController
   before_action :member_only, except: [:index, :search]
   before_action :check_availabililty
   respond_to :html, :xml, :json
+  respond_to :js, only: [:undo]
 
   def index
+    # XXX statement timeouts
     @post_versions = PostArchive.includes(:updater, post: [:versions]).search(search_params).paginate(params[:page], :limit => params[:limit], :search_count => params[:search])
     respond_with(@post_versions)
   end
@@ -13,14 +15,9 @@ class PostVersionsController < ApplicationController
 
   def undo
     @post_version = PostArchive.find(params[:id])
+    @post_version.undo!
 
-    if @post_version.post.visible?
-      @post_version.undo!
-    end
-
-    respond_with(@post_version) do |format|
-      format.js
-    end
+    respond_with(@post_version)
   end
 
   private