fix broken link [ci skip]
[ActiveJob] Add queue_name_prefix so all queue are prefixed .
We can split queues on a per environement basis as well as seggregate per application so we can split queues on a per env basis

ActiveJob::Base.queue_name_prefix = 'foo'
Merge pull request #16546 from aditya-kapoor/remove-broken-link

fix broken link to rails blog [ci skip]
Add activejob guide to documents.yml [ci skip]
Merge pull request #16539 from seuros/activejob

[ActiveJob] Add queue_name_prefix
Merge pull request #16547 from cristianbica/add-active-job-guide-links

Add activejob guide to documents.yml [ci skip]
Fixes the `Relation#exists?` to work with polymorphic associations.

Fixes #15821.
Fix broken link to Upgrading Ruby on Rails Guide

in the 4.2 Release Notes [skip ci]

Change to link suggested by @zzak [skip ci]
Merge pull request #16545 from jonatack/patch-9

Fix broken link to Upgrading Ruby on Rails Guide [ci skip]
Grammar pass

[ci skip]

Add improvements from @eileencodes [skip ci]
Fix after_commit warning message
Merge pull request #16548 from arthurnn/fix_warn_message

Fix after_commit warning message
Deprecate TagAssertion instead of removing
Removed warning
Point to unreleased deprecated_sanitizer
Remove to_s from reflection.type in add_constraints

The instance var is already saved as a string in the initialization
method of AssociationReflection.

See https://github.com/rails/rails/blob/master/activerecord/lib/active_record/reflection.rb#L273
Merge pull request #16550 from eileencodes/remove-unnecessary-to_s-from-add_constraints-method

Remove to_s from reflection.type in add_constraints
Merge pull request #16542 from seamusabshere/numerify-pool-checkout-timeout-from-urls-4-1-stable

Make sure :checkout_timeout and :dead_connection_timeout are numbers
Conflicts:
	activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
Make `AC::Params#to_h` return Hash with safe keys

`ActionController::Parameters#to_h` now returns a `Hash` with
unpermitted keys removed. This change is to reflect on a security
concern where some method performed on an `ActionController::Parameters`
may yield a `Hash` object which does not maintain `permitted?` status.
If you would like to get a `Hash` with all the keys intact, duplicate
and mark it as permitted before calling `#to_h`.

    params = ActionController::Parameters.new(name: 'Senjougahara Hitagi')
    params.to_h # => {}

    unsafe_params = params.dup.permit!
    unsafe_params.to_h # => {"name"=>"Senjougahara Hitagi"}

    safe_params = params.permit(:name)
    safe_params.to_h # => {"name"=>"Senjougahara Hitagi"}

This change is consider a stopgap as we cannot chage the code to stop
`ActionController::Parameters` to inherit from
`HashWithIndifferentAccess` in the next minor release.

Also, adding a CHANGELOG entry to mention that
`ActionController::Parameters` will not inheriting from
`HashWithIndifferentAccess` in the next major version.
Add missing `Hash` methods to `AC::Parameters`

This is to make sure that `permitted` status is maintained on the
resulting object.

I found these methods that needs to be redefined by looking for
`self.class.new` in the code.

* extract!
* transform_keys
* transform_values