Backport passing Resque::Worker object to before_first_fork hook

This is compatible with the current version of resque:

https://github.com/resque/resque/blob/50e6f3e26/lib/resque/worker.rb#L330

Needed to be able to pause workers when they boot instead of having
to reserve and requeue a job.
Merge pull request #2 from github/before-first-fork-backport

Backport passing Resque::Worker object to before_first_fork hook