Sidekiq 3.2.5 compatibility

Ah, gotta love monkey patching and internals poking... #not

Sidekiq 3 reorganized external error handlers as provider-specific classes (instead of the [per-provider methods](https://github.com/mperham/sidekiq/blob/v2.17.7/lib/sidekiq/exception_handler.rb#L20-L22) that we used to mock for testing). It also handles exceptions in providers, and tests were updated to reflect those changes

The patch's require was also updated because error handling is not universally included anymore.