Make sure restoration always happen.

* Grouped the valid test cases in one place
* Make the length of the generated password obvious
* Removed two wrong (copy-and-pasted) test cases

SecurePassword - Validate password must be less than or equal to 72

See #14591, Reason - BCrypt hash function can handle maximum 72 characters.

Fixes #15705.

Remove `serialized?` from the type interface

Fix request's path_info when a rack app mounted at '/'.

Open extension point for defining options in build_through_record

Remove unused `method_missing` definition

This fixes #15496

Add missing test cases for #assert_no_difference

prevent bad automatic inverse_of association

In actionview, eliminate calls to tag that use html_safe parameter values.

Fixes issue #15511.

Through associations should set both parent ids on join models

ActionController::Parameters#require now accepts FalseClass values

member = Member.new(club: Club.new)
member.save!

Before:

member.current_membership.club_id # => nil

After:

member.current_membership.club_id # => club's id

Detect in-place changes on mutable AR attributes

We have several mutable types on Active Record now. (Serialized, JSON,
HStore). We need to be able to detect if these have been modified in
place.

Remove unused column types override

We always define attribute methods in the constructor or in `init_with`.

Reorder test which does not represent real world usage

variables [ci skip]
Thanks to @matthewd for the excellent feedback! ❤

In actionview, eliminate calls to tag that use html_safe parameter values. This is generally unnecessary, since tag handles string quoting, except in one case (utf8_enforcer_tag) where we want to specify the encoding ourselves.

We don't generally modify our classes at runtime like this. Let's create
the instance after the class is created. Original commit doesn't imply
that this was intentional behavior.

This partially reverts commit 1a203d5e.

Reason: It was committed by accident

Rails 4.2 release notes [ci skip]

Ensure we always define attribute methods

Point to future 4-2-stable branch for detailed changes. [ci skip]

Sync Active Support changelogs with release notes [ci skip]

4.2 Release Notes is a work in progress [ci skip]

Assorted fixes for AS release notes [ci skip]

* `Hash#deep_transform_keys` has already been backported
* Mentioning `ActiveSupport::SafeBuffer#prepend` in the "Deprecations" section would be enough
* Fix syntax in `Kernel#concern` example

Sync AS release notes with the latest commits [ci skip]

Synced 4.2 release notes with commits in railties [ci skip]

Sync AP Deprecations and Notable changes from CHANGELOG [ci skip]

Removed 4.2 release notes from the index [ci skip]

This deprecation was reverted in 489a8f2a [ci skip]

Synced Active Record changelogs for 4.2 release notes [ci skip]

Synced Active Model changelog with the release notes [ci skip]

Added cc26b6b7 as a 'Removal' item in AP release notes [ci skip]

Use 'character' instead of 'symbol' to avoid confusion [ci skip]

Edit pass on 4.2 release notes [ci skip]

📝 💄 Use `.xyz` and `#xyz` appropiately [ci skip]

Introduce an Attribute object to handle the type casting dance

- image_tag is an instance method
- explain possible results when asset pipeline is used

Fixes #15685.