Fix documentation of extract_handler_and_format_and_variant [ci skip]

Fix to use custom join table in habtm

When used a custom join_table name on a habtm, rails was not saving it
on Reflections. This causes a problem when rails loads fixtures, because
it uses the reflections to set database with fixtures.

Fix code & improve grammar in "Forms to External Resources" [ci skip]

in the "Forms to External Resources" section [skip ci]

* master: (28 commits)
  move AR length validation tests into separate test-case.
  No need for trailing slash on migration path.
  reset `@arel` when modifying a Relation in place.
  PostgreSQL Timestamps always map to `:datetime`.
  [ci skip] Improve formatting and yml
  Fix a typo in the doc of forty_two AR FinderMethod
  Improve readability of contributing to rails guide. [ci skip]
  Precompile the image we're referencing, too.
  `ActiveRecord::Base.no_touching` no longer triggers callbacks or start empty transactions.
  Fixed an issue with migrating legacy json cookies.
  Correct comment [ci skip]
  Perfer to define methods instead of calling test
  Fix syntax error
  Add CHANGELOG entry for #14757 [ci skip]
  Fix run-on sentences and improve grammar [skip ci]
  Add test for using ActionView::Helpers::FormHelper.label with block and html
  select! renamed to avoid name collision Array#select!
  Rearrange deck chairs on the titanic. Organize connection handling test cases.
  Change favicon_link_tag helper mimetype from image/vnd.microsoft.icon to image/x-icon.
  ActionController::Renderers documentation fix
  ...

Conflicts:
	activerecord/test/cases/validations/association_validation_test.rb

Causes a double // in Dir.glob that breaks Ruby 2.2-trunk.
Not really a bug, but not relevant to this test either.

Originally added in ed21f0c5

/cc @tenderlove

PostgreSQL Timestamps always map to `:datetime`.

The PG Adapter should use `:datetime` consistently instead of mapping
mispellings to `:timestamp`.

See #14513

[ci skip] Improve formatting and yml

Fix a typo in the doc of forty_two AR FinderMethod [ci skip]

[ci skip] Improve readability of contributing to rails guide.

Fix railties asset tests: precompile the image we're referencing

You can't compile a file that references a non-compiled asset's path.

.. unless you turn off asset runtime errors.

Outside of a test case like this, `config.assets.precompile` would
normally retain its default entry, which precompiles all images (and
other non-JS/CSS files) that are in `app/assets`.

Move `NoTouching` down the inheritance chain on AR::Base

Closes #14841.

Fixed an issue with migrating legacy json cookies.

Previously, the `VerifyAndUpgradeLegacySignedMessage` assumes all incoming
cookies are marshal-encoded. This is not the case when `secret_token` is
used in conjunction with the `:json` or `:hybrid` serializer.

In those case, when upgrading to use `secret_key_base`, this would cause a
`TypeError: incompatible marshal file format` and a 500 error for the user.

Fixes #14774.

*Godfrey Chan*

Correct comment [ci skip]

This reverts commit 7f62f30f.

This file is using this pattern already

Fix behavior of select! to be consistent with select #14752

Properly handle scoping with has_many :through. Fixes #14537.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/associations/has_many_through_associations_test.rb

Fix inconsistent behavior from String#pluralize

Fix run-on sentences and improve grammar [skip ci]

Change favicon_link_tag helper mimetype from image/vnd.microsoft.icon to image/x-icon.

replace class_eval by define_method in abstract_controller/callbacks

Add test for using ActionView::Helpers::FormHelper.label with block and html