Notify with Bugsnag.notify TODO: looses tabs?

(cherry picked from commit 66f40255de4897691c7d8416243f3c71ce2c06a5)
Adapt to sidekiq error handling API (thanks @mperham)
Avoid instantiation, since we only need the method
Remove absolute consts: might not be necessary
Remove absolute consts that aren't needed
Merge branch 'sidekiq-3'

* sidekiq-3:
  Remove absolute consts that aren't needed