Preparing for 4.2.0.beta1 release
Use system /tmp when testing actionpack

https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
added support and enabled parallel execution of the actionpack tests.

However it introduced https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
since one cannot connect to a socket file that's inside a Vagrant synced folder
due to security restrictions, and DRb tries to.

Also rename the temporary files to make it obvious that they're rails-related,
since now they're placed outside the project's directory.

Fixes https://github.com/rails/rails/commit/c64bff2c87ebf363703c63ecd4a96d56a1a78364
[ci skip] Fix example code of ActiveRecord::FixtureSet.context_class
Don't rescue IPAddr::InvalidAddressError

IPAddr::InvalidAddressError does not exist in Ruby 1.9.3
and fails for JRuby in 1.9 mode.

As IPAddr::InvalidAddressError is a subclass of ArgumentError
(via IPAddr::Error) just rescuing ArgumentError is fine.
Merge pull request #16728 from splattael/invalid_address_error

Don't rescue IPAddr::InvalidAddressError
Merge pull request #16739 from y-yagi/patch-6

[ci skip] Fix example code of ActiveRecord::FixtureSet.context_class
Revert "Merge pull request #16254 from zuhao/refactor_activerecord_attribute_decorators_test"

This reverts commit 16fe19831548f108c113094d106663497fc190d5, reversing
changes made to 4c81c8ce533896be28bdc0b055ff30bb9dee1316.

The call to `Model.reset_column_information` was to express the intent of the test.
`reset_column_information` itself can trigger SQL queries because it checks
for a tables existance. Let's move it outside of the block.

/cc @sgrif
[ActiveJob] extract JobBuffer from helper
Merge pull request #16740 from seuros/activejob

[ActiveJob] extract JobBuffer from helper
Don't test PostgreSQL implementation details

Asserting that the message contains "QUERY PLAN" is enough for the adapter's test.
The plan may vary according to number of tuples etc. but that's out of our concern.
Some documentation fixes [ci skip]
Make test:isolated run without bundler for Action Mailer

Action Mailer tests weren't able to run in isolation without the bundle
exec prefix since we were requiring gems before requiring abstract_unit.

We don't need the `gem` call thus and the require_relative since the
test directory should be present in the load path when we run any test.
Avoid skipping Sidekiq tests on Rubinius

Now that Travis provides support for Rubinius 2.2.10, we can run the
Sidekiq tests against this version.
Merge pull request #16742 from robin850/rbx-aj-sidekiq

Avoid skipping Sidekiq tests on Rubinius
Merge pull request #16741 from robin850/am-isolated-wo-bundle

Make test:isolated run without bundler for Action Mailer
Don't allow AR::Tasks::DatabaseTasks.migrate to mutate Migration.verbose value

This fixes random test failure in migrator_test.rb
Fixed Active Job Backburner adapter
Merge pull request #16746 from cristianbica/fix-backburner-adapter

Fixed Active Job Backburner adapter
Merge branch 'master' of github.com:rails/rails
Added yield to Object#presence