`oldie = 'true'` to `tinyint(1)` column is invalid value for MySQL:

```
Mysql2::Error: Incorrect integer value: 'true' for column 'oldie' at row 1: update horses set oldie = 'true'
```

Update plugin_generator.rb

Fix activesupport/CHANGELOG.md [ci skip]

Fix migration version in doc of #up_only

Performance improvements for add_method_to_attributes!

* Add a #populate method to migrations

* Address rubocop issues

* Rename to #up_only and use #execute in the examples intead of the model

* Update CHANGELOG

[Rich Daley & Rafael Mendonça França]

CI against JRuby 9.1.14.0

JRuby 9.1.14.0 has been released and this version is available on Travis CI.
http://jruby.org/2017/11/08/jruby-9-1-14-0

Update `exists?` documentation [ci skip]

Update layouts_and_rendering.md  [ci skip]

Make it clear that `exists?` can be chained onto a relation

Ensure plugin_generator adds to new line in Gemfile, even if the Gemfile
does not end with an empty line.

[Lisa Ugray, Nikita Penzin]

Disallow raw SQL in dangerous AR methods

Compression has long been available, but opt-in and at a 16kB threshold.
It wasn't enabled by default due to CPU cost. Today it's cheap and
typical cache data is eminently compressible, such as HTML or JSON
fragments.

Compression dramatically reduces Memcached/Redis mem usage, which means
the same cache servers can store more data, which means higher hit
rates.

To disable compression, pass `compress: false` to the initializer.

Currently the environment is not loaded in some db tasks.
Therefore, if use encrypted secrets values in `database.yml`,
`read_encrypted_secrets` will not be true, so the value can not be
used correctly.

To fix this, added `environment` as dependency of `load_config`.
It also removes explicit `environment` dependencies that are no longer
needed.

Fixes #30717

* Supports vanilla Redis, hiredis, and Redis::Distributed.
* Supports Memcached-like sharding across Redises with Redis::Distributed.
* Fault tolerant. If the Redis server is unavailable, no exceptions are
  raised. Cache fetches are treated as misses and writes are dropped.
* Local cache. Hot in-memory primary cache within block/middleware scope.
* `read_/write_multi` support for Redis mget/mset. Use Redis::Distributed
  4.0.1+ for distributed mget support.
* `delete_matched` support for Redis KEYS globs.

Cache regexps generated from acronym_regex

Sort mailer previews alphabetically

Closes #31138.

fix bug on added? method

The documentation claims that given values go through "normal AR type
casting and serialization", which to me implies
`serialize(cast(value))`, not just serialization. The docs were changed
to use this wording in #22492. The tests I cited in that PR (which is
the same test modified in this commit), is worded in a way that implies
it should be using `cast` as well.

It's possible that I originally meant "normal type casting" to imply
just the call to `serialize`, but given that `update_all(archived:
params['archived'])` seems to be pretty common, I'm inclined to make
this change as long as no tests are broken from it.

Do not use `Arel.star` when `ignored_columns`

Make clear that the files are not to be run for interpreters.

Fixes #23847.
Fixes #30690.
Closes #23878.

If there are any ignored columns, we will now list out all columns we
want to be returned from the database.

Includes a regression test.

fix rubocop issues

Make sidekiq and resque integration tests work in ci

Since 8f2490b5, the integration test of sidekiq and resque is not working
in CI.
https://travis-ci.org/rails/rails/jobs/301276197#L2055
https://travis-ci.org/rails/rails/jobs/301276197#L2061

Because 8f2490b5 removed password from `redis-server`.
So must also remove passwords from these tests.

Add new error class `StatementTimeout` which will be raised when statement timeout exceeded (#31129)

We are sometimes using The MAX_EXECUTION_TIME hint for MySQL depending
on the situation. It will prevent catastrophic performance down by wrong
performing queries.

The new error class `StatementTimeout` will make to be easier to handle
that case.

https://dev.mysql.com/doc/refman/5.7/en/optimizer-hints.html#optimizer-hints-execution-time