add a sitesetting to enable the CleanUpUploads job

app/jobs/scheduled/clean_up_uploads.rb

@@ -4,6 +4,7 @@ module Jobs
     recurrence { hourly }
 
     def execute(args)
+      return unless SiteSetting.clean_up_uploads?
 
       uploads_used_in_posts = PostUpload.uniq.pluck(:upload_id)
       uploads_used_as_avatars = User.uniq.where('uploaded_avatar_id IS NOT NULL').pluck(:uploaded_avatar_id)
@@ -13,8 +14,7 @@ module Jobs
       Upload.where("created_at < ?", grace_period.hour.ago)
             .where("id NOT IN (?)", uploads_used_in_posts + uploads_used_as_avatars)
             .find_each do |upload|
-        # disable this for now.
-        #upload.destroy
+        upload.destroy
       end
 
     end

app/models/site_setting.rb

@@ -184,6 +184,7 @@ class SiteSetting < ActiveRecord::Base
   setting(:enforce_global_nicknames, true)
   setting(:discourse_org_access_key, '')
 
+  setting(:clean_up_uploads, false)
   setting(:uploads_grace_period_in_hours, 1)
   setting(:enable_s3_uploads, false)
   setting(:s3_access_key_id, '')

config/locales/server.en.yml

@@ -619,6 +619,7 @@ en:
 
     suggested_topics: "Number of suggested topics shown at the bottom of a topic"
 
+    clean_up_uploads: "Remove orphaned uploads to prevent illegal hosting. WARNING: you might want to make a backup of your /uploads directory before enabled this setting."
     uploads_grace_period_in_hours: "Grace period (in hours) before an orphan upload is removed."
     enable_s3_uploads: "Place uploads on Amazon S3"
     s3_upload_bucket: "The Amazon S3 bucket name that files will be uploaded into. WARNING: must be lowercase (cf. http://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html)"