Ensure compatibility between ActionDispatch::Request::Session and Rack

Adding the `each` method is required for ensuring compatibility between
Rails, and other Rack frameworks (like Sinatra, etc.), that are mounted
within Rails, and wish to use its session tooling. Prior to this, there
was an inconsistency between ActionDispatch::Request::Session and
Rack::Session::Cookie, due to the absence of the `each` method. This
should hopefully fix that error. :)

For a full integration test with Sinatra and a standalone Rack
application, you can check out the gist for that here: https://gist.github.com/maclover7/08cd95b0bfe259465314311941326470.

Solves #15843.

Bump Ruby versions

Fix some typos in comments [ci skip]

[ci skip]

2.2.4 --> 2.2.5
2.3.0 --> 2.3.1

This is an engine living in action_cable/engine.rb, convention is to
call these things *::Engine.

Looking at thi git history looks like the current *::Railtie was just
an accident.

Fix actionpack typos [ci skip]

Depend on bundler 1.11.2 on travis until bundle update discrepancy is solved on 1.12.x

Fix failing tests

Change RangeError to a more specific ActiveModel::RangeError

The should make it easier for apps to rescue ActiveModel specific
errors without the need to wrap all method calls with a generic
rescue RangeError.

Release notes: Remove duplicate entries

- Removed duplicate entry for collection caching.
- The entry was duplicate and the link to PR was also wrong.
- Consolidated entries for `belongs_to` required by default.

Fix small typo in Active Record Migrations documentation

remove `empty?` from CHANGELOG [ci skip]

Follow up to 98264a13

Resolved by https://github.com/ruby-concurrency/concurrent-ruby/pull/529

Fixes #24627.

Unlike `one?` and `none?`, `empty?` has interactions with methods
outside of enumerable. It also doesn't fit in the same vein.
`Topic.any?` makes sense. `Topic.empty?` does not, as `Topic` is not a
container.

Fixes #24808
Close #24812

[ci skip] Fix ActionCable README

default worker pool size was changed from 100 to 4 at #24376

Add `:nodoc:` to `schema_creation` [ci skip]

`schema_creation` is not public API.

https://github.com/rails/rails/blob/v5.0.0.beta4/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb#L121
https://github.com/rails/rails/blob/v5.0.0.beta4/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb#L78

Fix counter_cache double increment bug

Close #24183

Guides should be updated because ActionDispatch::LoadInterlock was replaced with
ActionDispatch::Executor at #23807.

Signed-off-by: NJeremy Daer <jeremydaer@gmail.com>

fix incorrect module name [ci skip]

Fix grammar. [ci skip]

Replace `Rails.version.to_f` with Active Record

Fix actionpack typos [ci skip]

Rails should not be explicity mentioned within Active Record, since
railties and the Rails ecosystem is not required for use.

Signed-off-by: NJeremy Daer <jeremydaer@gmail.com>