According to pr #22443 in the guides there's always a dollar sign before every command, so why is in the main README a `$` and in every submodule a `%`?

Just eye candy..

Replace ActionMailer::Base.respond_to? with respond_to_missing?

Fix the Railties tests

Railsties tests are broken with this new update checker so we will use
the old one until we have the tests fixed.

Related with e62ddac0

Related with 668c006c.

Remove old comment about AC::Parameters>subclasses

[ci skip]

Q: What happens if you initialize an AR model by passing Parameters that
have not been whitelisted with `permit`?

A: An `ActiveModel::ForbiddenAttributesError` is raised.

I think this behavior is correct, and it's better than what used to happen,
with unpermitted parameter being simply ignored.

Fix failing test using custom file watcher

Revert "don't start a new process for every test file"

This reverts commit 5a0e0e72.

This commit causes railties tests on TravisCI to always return a 0 status (all tests passing), even when tests are failing. Reverting for now until a new solution can be found.

LoadingTest#test_does_not_reload_constants_on_development_if_custom_file_watcher_always_returns_false in railties/test/application/loading_test.rb is failing with: `NoMethodError: undefined method 'execute' for #<#<Class:0x00000002465a30>:0x00000001f79698>`

The test creates an anonymous class to be used as a custom file watcher using `config.file_watcher=`. Per the Rails guides for Configuring, the class set to `config.file_watcher` “Must conform to ActiveSupport::FileUpdateChecker API”. Per the docs for ActiveSupport::FileUpdateChecker, the API depends on four methods: #initialize, #updated?, #execute, and #execute_if_updated. The custom file watcher in the failing test only implements the first two methods.

This pull request adds #execute and #execute_if_updated to the custom file_watcher, conforming it to the ActiveSupport::FileUpdateChecker API, and passing the test.

This will also get the defaults from attribute definitions like:

     attribute :type, :string, default: "SomethingElse"

`has_attribute?` method to check wether a given attribute has been defined.

This solves the following error:

     ActiveRecord::StatementInvalid: Could not find table 'guitars'

It seems that the table structure of the `Guitar` model has not been
necessary until now. Due to the wrong table name the model was not
correctly linked to the table.

STI cast new instances to `default type` on initialize.

fixes #17121

Update autoloading_and_reloading_constants.md

It appears that I missed this one when I delegated all the non-mutation
array methods that were not on Enumerable

Fixed a typo

Modify unscoped usage guide to include chaining [ci skip]

Explain the connection pool error message better [ci skip]

rescue memcached errors in a consistent way

The previous message was misleading (especially for Ops guys) when
diagnosing problems related to the database connection.

The message was suggesting that the connection cannot be obtained which
normally assumes the need to look at the database.

But this isn't the case as the connection could not be retrieved from
the application's internal connection pool.

The new message should make it more explicit and remove the confusion.

Allow use of minitest-rails gem with test runner

Fix rake db:structure:dump on Postgres when multiple schemas are used

Conflicts:
	activerecord/CHANGELOG.md

Closes #22346.

Refactor `AbstractAdapter#initialize`

Fix indentation in CHANGELOG.md [ci skip]

`pool` in args is unused anymore. And `config` is used in all adapters.

Move some bind related test cases from finder_test.rb to sanitize_t…

Document message validation option accepts Proc [ci skip]

Add `Routing` namespace to point appropriate constant

Bugfix collection association #create method