support rails 4 and sidekiq 3

transaction_include_action? was removed in rails 4, but new api is consistent with 3.2 anyway

so now Reactor::Publishable conditional events are calculated in their own after_commit block
thus allowing us to maintain feature parity for both rails 3.2 and 4
(due to the API change for after_commit declarations)
Merge pull request #6 from hired/feature/rails4sidekiq3

support rails 4 and sidekiq 3