Remove varargs from `Object#in?`

Same rationale as previous revert.

This reverts commit 887225e6.

It is not in the contract that flags have to be singletons,
the use of regular font indicates that.

This reverts commit 80036f9a.

This reverts commit ebf69ab1.

`in?` must not take multiple parameters because its behavior would be
ambiguous:

    # Test if "B" is included in a list of names with `"B".in?(*names)`:
    names = ["BMorearty"]
    "B".in?(*names)   # => true

    names = ["BMorearty","rubyduo"]
    "B".in?(*names)   # => false

Conflicts:
	activesupport/lib/active_support/core_ext/object/inclusion.rb
	activesupport/test/core_ext/object/inclusion_test.rb

failure to parse params should trigger a 400 Bad Request

Fix noisy output when running rake db:schema:load on postgreSQL and structure.sql

activerecord/lib/active_record/associations.rb states:

    # [association=(associate)]
    #   Assigns the associate object, extracts the primary key, sets it as the foreign key,
    #   and saves the associate object.

Since commit 42dd5d9f to fix #7191, this
is no longer the case if the associate has changed, but is the same
object. For example:

    # Pirate has_one :ship
    pirate = Pirate.create!(catchphrase: "A Pirate")
    ship = pirate.build_ship(name: 'old name')
    ship.save!

    ship.name = 'new name'
    pirate.ship = ship

That last line should trigger a save. Although we are not changing the
association, the associate (ship) has changed.

Added :nodoc: for relation.rb's private methods

Merge pull request #10389 from wangjohn/removing_the_app_constant_and_replace_with_rails_application_instance

Removing the app constant and replacing it with Rails.application

syntax. This helps removing the class level abstraction of an
application.

remove unused require

add missing semicolon to journey parser.y

Abort a rake task when missing db/structure.sql like `db:schema:load` task.

Rack::Mount was replaced by Journey, Fixed comment

* it's Action Mailer not ActionMailer
* it's Action Pack not ActionPack
* it's Active Support not ActiveSupport

/cc @fxn

/cc @fxn

Minor code duplication removed

Make `rake doc:guides` works again.  Fix #10384.

Moved update_record logic to relation.rb

add missing :nodoc: marks to ActiveRecord::Delegation [ci skip]

Fix assets precompiling in production guide