Tweak when we include the AR transaction callback rescuing

[apalmblad]

Goal

Bugsnag notifies when we see an exception in a transaction (or rollback) callback. This is unnecessary as Rails now raises exceptions out of transaction callbacks. This Bugsnag behaviour means that certain errors are always sent to bugsnag instead of potentially handled elsewhere.

Bugsnag behaviour can be seen here: https://github.com/apalmblad/bugsnag-ruby/blob/master/lib/bugsnag/integrations/rails/active_record_rescue.rb#L14

Rails has stopped swallowing exceptions in these callbacks, making in configurable in Rails 4, and then the default behaviour in Rails 5.
Rails allowing exceptions to be raised
Rails 5 removing configuration for not raising callback exceptions

Design

To minimize changes needed, I consider the rails version and the various configuration values and conditionally include the file.

Changeset

The rails integration behaviour was changed, and we stop including it.

Testing

I've added a spec to check whether or not its included.

[Jaacky]

Suggested change

	if Rails::VESION::MAJOR == 4
	if ActiveRecord::Base.errors_in_transactional_callbacks == :raise
	require "bugsnag/integrations/rails/active_record_rescue"
	include Bugsnag::Rails::ActiveRecordRescue
	end
	elsif Rails::VESION::MAJOR < 4
	if Rails::VERSION::MAJOR == 4
	if ActiveRecord::Base.errors_in_transactional_callbacks == :raise
	require "bugsnag/integrations/rails/active_record_rescue"
	include Bugsnag::Rails::ActiveRecordRescue
	end
	elsif Rails::VERSION::MAJOR < 4

[imjoehaines]

Thanks for the PR, @apalmblad!

I'll merge this in #717, where I've added tests to our Rails test apps to get better coverage of this behaviour

[apalmblad]

Thanks for putting this in.

[xljones]

Released in https://github.com/bugsnag/bugsnag-ruby/releases/tag/v6.24.2 🎉 , thanks for the contribution!