Closes #13146.

This fixes an error when using:

```
change_colum :table, :column, :bigint, array: true
```

This commit takes into account the last cache_enabled value, before clearing query_cache.

Fixture files are passed through an ERB renderer before being read as
YAML. The rendering is currently done in the context of the main object,
so method definitons leak into other fixtures, and there is no clean
place to define fixture helpers.

After this commit, the ERB renderer will use a new subclass of
ActiveRecord::FixtureSet.context_class each time a fixture is rendered.

Previously, the `has_one` macro incorrectly accepts the `counter_cache` option
due to a bug, although that options was never supported nor functional on
`has_one` and `has_one ... through` relationships. It now correctly raises an
`ArgumentError` when passed that option.

For reference, this bug was introduced in 52f8e4b9.

also clarify native rename_index support is >= 5.7, not > 5.7

Extract **notable changes**, **deprecations** and **removals** from
each CHANGELOG.

I tried to reference the commits and pull requests for new features
and deprecations.

In the process I also made some minor changes to the CHANGELOGS.

The 4_1_release_notes guide is declared WIP.

Fix bug when validating the uniqueness of an aliased attribute.
Conflicts:
	activerecord/CHANGELOG.md

This prevents the following error when a MySQL index on a foreign key
column is renamed:

```
ActiveRecord::StatementInvalid: Mysql2::Error: Cannot drop index 'index_engines_on_car_id': needed in a foreign key constraint: DROP INDEX `index_engines_on_car_id` ON `engines`
```

refs: #13038.

Fixes #12812
Raise `ActiveRecord::RecordNotDestroyed` when a child marked with
`dependent: destroy` can't be destroyed.

The following code:
```ruby
class Post < ActiveRecord::Base
  has_many :comments, dependent: :destroy
end

class Comment < ActiveRecord::Base
  before_destroy do
    return false
  end
end

post = Post.create!(comments: [Comment.create!])
post.comments = [Comment.create!]
````

would result in a `post` with two `comments`.
With this commit, the same code would raise a `RecordNotDestroyed`
exception, keeping the `post` with the same `comment`.

Also make Action Mailer changelog format more consistent with the
others [ci skip]

I'm pretty confused about the addition of this method. The documentation
says that it was intended to allow the removal of values from the
default scope (in contrast to #except). However it behaves exactly the
same as except: https://gist.github.com/jonleighton/7537008 (other than
having a slightly enhanced syntax).

The removal of the default scope is allowed by
94924dc3, which was not a change we
could make until 4.1 due to the need to deprecate things. However after
that change #unscope still gives us nothing that #except doesn't already
give us.

However there *is* a desire to be able to unscope stuff in a way that
persists across merges, which would allow associations to be defined
which unscope stuff from the default scope of the associated model. E.g.

  has_many :comments, -> { unscope where: :trashed }

So that's what this change implements. I've also corrected the
documentation. I removed the guide references to #except as I think
unscope really supercedes #except now.

While we're here, there's also a potential desire to be able to write
this:

  has_many :comments, -> { unscoped }

However, it doesn't make sense and would not be straightforward to
implement. While with #unscope we're specifying exactly what we want to
be removed from the relation, with "unscoped" we're just saying that we
want it to not have some things which were added earlier on by the
default scope. However in the case of an association, we surely don't
want *all* conditions to be removed, otherwise the above would just
become "SELECT * FROM comments" with no foreign key constraint.

To make the above work, we'd have to somehow tag the relation values
which get added when evaluating the default scope in order to
differentiate them from other relation values. Which is way too much
complexity and therefore not worth it when most use cases can be
satisfied with unscope.

Closes #10643, #11061.

This fixes a bug when merging relations of different classes.

```
Given:
  Post.joins(:author).merge(Author.order(name: :desc)).to_sql

Before:
 SELECT "posts".* FROM "posts"
   INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
   ORDER BY "posts"."name" DESC

After:
 SELECT "posts".* FROM "posts"
   INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
   ORDER BY "authors"."name" DESC
```

This reverts commit 22f80ae5.

See
https://github.com/rails/rails/commit/22f80ae57b26907f662b7fd50a7270a6381e527e#commitcomment-4640676

Conflicts:
	activerecord/CHANGELOG.md

when destroying a record on a has_many :through association.
:destroy method has own counter_cache callbacks.

* A non-zero exit status allows subsequent shell commands to be chained
  together such as: `rake db:reset test:prepare && rspec && cap deploy`
  (if you're feeling brave :)
* Any exceptions raised during the `create` and `drop` tasks are caught
  in order to print a "pretty" message to the user. Unfortunately doing
  so prevents rake from aborting with a non-zero exit status to the shell.
* Therefore we re-raise the exceptions after the "pretty" message and
  re-catch them in the task.
* From the task we explicitly exit with a non-zero status. This method
  was chosen (rather than just letting rake fail from the exception) so
  that the backtrace is suppressed and the output to stderr is
  unchanged.
* Update activerecord CHANGELOG

The log output used to be confusing in situation where type casting has
"unexpected" effects. For example when finding records with a `String`.

BEFORE:

irb(main):002:0> Event.find("im-no-integer")
D, [2013-11-09T11:10:28.998857 #1706] DEBUG -- :   Event Load (4.5ms)  SELECT "events".* FROM "events" WHERE "events"."id" = $1 LIMIT 1  [["id", "im-no-integer"]]

AFTER:

irb(main):002:0> Event.find("im-no-integer")
D, [2013-11-09T11:10:28.998857 #1706] DEBUG -- :   Event Load (4.5ms)  SELECT "events".* FROM "events" WHERE "events"."id" = $1 LIMIT 1  [["id", 0]]

Revert "ActiveRecord::Base#<=> has been removed.  Primary keys may not be in order," -- will be replaced with a check to ensure that the keys used for comparison are integers, and only fail if they are not.

This reverts commit 6256734e.

Conflicts:
	activerecord/CHANGELOG.md

Extend ActiveRecord::Base#cache_key to take an optional list of timestamp attributes of which the highest will be used.

Added ActiveRecord::Base#enum for declaring enum attributes where the values map to integers in the database, but can be queried by name

was using nullify strategy

This caused a regression in applications trying to upgrade.

Also if the user set the dependent option as destroy he expects to get
the records removed from the database.