Merge pull request #14843 from tgxworld/improve_readability_of_contributing_to_rails_guide

[ci skip] Improve readability of contributing to rails guide.
Fixes Issue #13466.

Changed the call to a scope block to be evaluated with instance_eval.
The result is that ScopeRegistry can use the actual class instead of base_class when
caching scopes so queries made by classes with a common ancestor won't leak scopes.
Fix a typo in the doc of forty_two AR FinderMethod
Merge pull request #14858 from ebouchut/patch-1

Fix a typo in the doc of forty_two AR FinderMethod [ci skip]
[ci skip] Improve formatting and yml
Merge pull request #14856 from Gaurav2728/gaurav-typo_fix

[ci skip] Improve formatting and yml
PostgreSQL Timestamps always map to `:datetime`.

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

See #14513
Merge pull request #14859 from jefflai2/datetime_type

PostgreSQL Timestamps always map to `:datetime`.
reset `@arel` when modifying a Relation in place.

/cc @tenderlove
No need for trailing slash on migration path.

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 ed21f0c50270139ddb6993acfdaea4586ffd09a3
move AR length validation tests into separate test-case.

Conflicts:
	activerecord/test/cases/validations/association_validation_test.rb
Merge branch 'master' into adequaterecord

* 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
  ...
Grammar and formatting fixes in Form Helpers Guide

Improved version of #14851 after helpful feedback from @robin850 and @matthewd.

[skip ci]
Fix code & grammar in Form Helpers Guide

in the "Forms to External Resources" section [skip ci]
Merge pull request #14873 from jonatack/patch-8

Fix code & improve grammar in "Forms to External Resources" [ci skip]
Fix custom join_table name on habtm reflections

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.
Merge pull request #14853 from kassio/kb-fix-custom-join-table-habtm

Fix to use custom join table in habtm
Warning removed for missmatched indentation
Fix documentation of extract_handler_and_format_and_variant [ci skip]
Merge pull request #14875 from prathamesh-sonpatki/fix-extract-handler-format-variant-doc

Fix documentation of extract_handler_and_format_and_variant [ci skip]