In particular, `.new`, `#update`, `#merge`, `#replace` all accept
objects which respond to `#to_hash`, even if those objects are not
Hashes directly.

Swap Timestamp/Callbacks order in ActiveRecord::Base

Adds explanation of :base attribute to errors.add [ci skip]

[ci skip]

AR .persisted? throws SystemStackError for an unsaved model with a
custom primary_key that didn't save due to validation error

custom primary_key that didn't save due to validation error

ActiveRecord/ActiveModel '#validate' alias for 'valid?'

It's unintuitive to call '#valid?' when you want to run validations but
don't care about the return value.

The alias in ActiveRecord isn't strictly necessary (the ActiveModel
alias is still in effect), but it clarifies.

When the tests are executed in order, the dependency is loaded at the right time.
However this makes it impossible to execute a single test later down the line.
Let's require the dependecy at the beginning to get them working independent of the order.

This resolves the following error:

```
$ ARCONN=postgresql ruby -Itest /Users/senny/Projects/rails/activerecord/test/cases/xml_serialization_test.rb -n test_to_xml
Using postgresql
Run options: -n test_to_xml --seed 51819

E

Finished in 0.081320s, 12.2971 runs/s, 0.0000 assertions/s.

  1) Error:
DatabaseConnectedXmlSerializationTest#test_to_xml:
NameError: uninitialized constant DatabaseConnectedXmlSerializationTest::REXML
    /Users/senny/Projects/rails/activerecord/test/cases/xml_serialization_test.rb:226:in `test_to_xml'
```

/cc @tgxworld fyi

This will keep the test suite passing with older PG installations.

Add a test case for save(validate: false) with invalid foreign key.

It is supposed to raise ActiveRecord::InvalidForeignKey when the
database has a fk constraint.

This method is not being called anywhere in our code and a GitHub search
show it is not being used in any project.

* cache `o.name` value
* Avoid extra `concat` call
* Avoid extra `<<` call

These comments will likely be outdated with time and doesn't include
any information that can't be found in the adapters

Also improve some of the code conventions

Create indexes inline in CREATE TABLE for MySQL

[ci skip] Fix Pull Request URL in 4.1 release note.

Also:
  - updates tests by stubbing table_exists? method
  - adds entry for creating indexes in CREATE TABLE to changelog

This is important, because adding an index on a temporary table after
it has been created would commit the transaction

Conflicts:
	activerecord/CHANGELOG.md

[ci skip]

Still touch associations when theres no timestamp

This reverts commit 6e3ab3e1, reversing
changes made to 39e07b64.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/autosave_association_test.rb

Generating proper migration when ActiveRecord::Base.pluralize_table_names = false

  ActiveRecord::Base.pluralize_table_names = false.

  Previously, generation a migration like this:

      rails g migration add_column_name_to_user name

  would not generating the correct table name.

Fixes #13426.

Support the options methods in tests