Reload doesn't clear attempts or last error when used with ActiveRecord backend

[Niels Meersschaert]

DelayedJob ActiveRecord 4.0.3 doesn't allow mass assignment of several attributes. As a result, the reload button doesn't reset the job as much as it wants to. Specifically

attr_accessible :priority, :run_at, :queue, :payload_object,
:failed_at, :locked_at, :locked_by, :handler

So, attempts and last_error aren't reset. Due to the backoff in DelayedJob, not being able to change attempts is a problem.