Allow unscope to work with `where.not`

Allows you to call #unscope on a relation with negative equality operators,
i.e. Arel::Nodes::NotIn and Arel::Nodes::NotEqual that have been generated
through the use of where.not.

Raise an exception when model without primary key calls .find_with_ids

Remove extra variable creation and merge.

Instrument the generation of Action Mailer messages

The processing of outbound mail is instrumented with the key
`process.action_mailer`. The payload includes the mailer name as well as
the mailer method.

In Relation#empty? use #exists? instead of #count.

avoid deprecation warning in sample code [ci skip]

Convert Fixnum into String the port number like `db:structure:dump` task in MySQL.

Account.find(1, lock: true)
-> DEPRECATION WARNING: Passing options to #find is deprecated. Please build a scope and then call #find on it.

Small cleanup on autosave association

Add sass globbing to asset pipeline docs [ci skip]

[ci skip]

[ci skip] Fix number of methods added by association.

Ensure ActionView::Digestor.cache is correctly cleaned up

Fix typo in form_helper.rb

add a new local variable to track if digests are being stored, to ensure the cleanup works correctly

Also clean up some trailing spaces on line 1143-1146.

Rephrase ActiveRecord transaction rollback warning [ci skip]

[ci skip]

Fix code blocks identation on AR and AS CHANGELOGs

Removing unused fake models from actionpack tests

[ci skip]

Conflicts:
	activerecord/lib/active_record/relation/finder_methods.rb

Pluck on NullRelation should accept a list of columns

This reverts commit 49f513c2.

Reason: Changelogs aren't supposed to be edited in docrails.