* Remove contention between multiple workers by performing an update to lock a job before fetching it
* Job payloads may implement #max_attempts to control how many times it should be retried
* Fix for loading ActionMailer extension
* Added 'delayed_job_server_role' Capistrano variable to allow delayed_job to run on its own worker server
    set :delayed_job_server_role, :worker
* Fix `rake jobs:work` so it outputs to the console