Add TIP about app:update task in 'A Guide for Upgrading Ruby on Rails'

Add changelog for #24542

Fixed ActionCable::Connection::ClientSocketTest test

Restore Hash#transform_keys behavior to always return a Hash instance

This brings the behavior more inline with other similar cases, such as
receiving a hash when an array of scalars was expected. Prior to this
commit, the key would be present, but the value would be `nil`

Fix broken link in 'Ruby on Rails 4.0 Release Notes'

- Fixed ActionCable::Connection::ClientSocketTest that was overriding ActionCable::Connection::StreamTest test name
- Only add attr_readers for required attributes

update example to specify the Action Cable mount path [ci skip]

Follow up to 8b69f1ee

[ci skip]

Should keep quoting behaivor of a time column value in sqlite3 adapter

Follow up to #24542.

In MySQL and PostgreSQL, a time column value is saved as ignored the
date part of it. But in SQLite3, a time column value is saved as a string.

We should keep previous quoting behavior in sqlite3 adapter.

```
sqlite> CREATE TABLE "foos" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "start" time(0), "finish" time(4));
sqlite> INSERT INTO "foos" ("start", "finish") VALUES ('2000-01-01 12:30:00', '2000-01-01 12:30:00.999900');
sqlite> SELECT "foos".* FROM "foos";
1|2000-01-01 12:30:00|2000-01-01 12:30:00.999900
sqlite> SELECT  "foos".* FROM "foos" WHERE "foos"."start" = '2000-01-01 12:30:00' LIMIT 1;
1|2000-01-01 12:30:00|2000-01-01 12:30:00.999900
sqlite> SELECT  "foos".* FROM "foos" WHERE "foos"."start" = '12:30:00' LIMIT 1;
sqlite>
```

Run Action Cable callbacks through the worker pool

MariaDB documentation [ci skip]

Add `quoted_time` for truncating the date part of a time column value

Context #24522.

TIME column on MariaDB doesn't ignore the date part of the string when
it coerces to time.

```
root@localhost [test] > CREATE TABLE `foos` (`id` int AUTO_INCREMENT PRIMARY KEY, `start` time(0), `finish` time(4)) ENGINE=InnoDB;
Query OK, 0 rows affected (0.02 sec)

root@localhost [test] > INSERT INTO `foos` (`start`, `finish`) VALUES ('2000-01-01 12:30:00', '2000-01-01 12:30:00.999900');
Query OK, 1 row affected, 2 warnings (0.00 sec)

Note (Code 1265): Data truncated for column 'start' at row 1
Note (Code 1265): Data truncated for column 'finish' at row 1
root@localhost [test] > SELECT `foos`.* FROM `foos`;
+----+----------+---------------+
| id | start    | finish        |
+----+----------+---------------+
|  1 | 12:30:00 | 12:30:00.9999 |
+----+----------+---------------+
1 row in set (0.00 sec)

root@localhost [test] > SELECT  `foos`.* FROM `foos` WHERE `foos`.`start` = '2000-01-01 12:30:00' LIMIT 1;
Empty set (0.00 sec)

root@localhost [test] > SELECT  `foos`.* FROM `foos` WHERE `foos`.`start` = '12:30:00' LIMIT 1;
+----+----------+---------------+
| id | start    | finish        |
+----+----------+---------------+
|  1 | 12:30:00 | 12:30:00.9999 |
+----+----------+---------------+
1 row in set (0.00 sec)
```

Test against MariaDB 10.0

[ci skip] Remove extra `so` from the Action Pack CHANGELOG

- Specify we want to run on latest stable ruby for mariadb

- change in runs of builds

Make mariadb? method publicly available

 :nodoc: version method.

Update ActionMailer base documentation [ci skip]

Alternate implementation of #24162 with tests. The code had diverged
too far on master to pull that implemenation directly.

Fixes #23778
Close #24162

[Mattew Draper & Sean Griffin]

Fixed bug introduced in #24519. Makes build green again

Add ruby 2.2.2+ version requirement for Rails 5 apps

Switch to keyword args for attribute_changed?

Previously we were assuming that the only valid types for encoding were
arrays and hashes. However, any JSON primitive is an accepted value by
both PG and MySQL.

This does involve a minor breaking change in the handling of `default`
in the schema dumper. This is easily worked around, as passing a
hash/array literal would have worked fine in previous versions of Rails.
However, because of this, I will not be backporting this to 4.2 or
earlier.

Fixes #24234

[ci skip]

 Reason:
 - Its not publicly used method.
 - Exposing it makes an assumption that other adapters support it based on its usage - ActiveRecord::Base.connection.version

 [ci skip]

We are using compare_without_coercion.

extension synonyms yml and yaml

Generate `cable.js` file if does not exist when generating channel

prevent 'attribute_changed?' from returning nil