New Lighthouse Tickets

I have added three new Lighthouse tickets.

1. Fix ActiveSupport::Cache::FileStore#cleanup to not be completely
broken (https://rails.lighthouseapp.com/projects/8994/tickets/6308)

2. Update Rails Guide to accurately describe the cache store changes
in 3.0 (https://rails.lighthouseapp.com/projects/8994/tickets/6309)

3. Update Rails Guide to describe after transaction callbacks on
ActiveRecord added in 3.0 (https://rails.lighthouseapp.com/projects/
8994/tickets/6310)