The Unicorn master resets any signal handlers and prevents rbtrace
from working properly as a result. Move the `require 'rbtrace'` call
to the Unicorn `after_fork` block and keep the initializer only for Sidekiq.
This will be enabled if ENABLE_RBTRACE environment variable is defined.
This will allow us to debug all sorts of issues in production:
https://github.com/tmm1/rbtrace