Do not take screenshot when test skipped

Also correct use of `direct class:` to `resolve` in example.

Correctly dump native timestamp types for MySQL

The native timestamp type in MySQL is different from datetime type.
Internal representation of the timestamp type is UNIX time, This means
that timestamp columns are affected by time zone.

```
> SET time_zone = '+00:00';
Query OK, 0 rows affected (0.00 sec)

> INSERT INTO time_with_zone(ts,dt) VALUES (NOW(),NOW());
Query OK, 1 row affected (0.02 sec)

> SELECT * FROM time_with_zone;
+---------------------+---------------------+
| ts                  | dt                  |
+---------------------+---------------------+
| 2016-02-07 22:11:44 | 2016-02-07 22:11:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)

> SET time_zone = '-08:00';
Query OK, 0 rows affected (0.00 sec)

> SELECT * FROM time_with_zone;
+---------------------+---------------------+
| ts                  | dt                  |
+---------------------+---------------------+
| 2016-02-07 14:11:44 | 2016-02-07 22:11:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)
```

Deprecate the EventedRedis subscription adapter

Unlike Faye support, it seems a bit too documented to remove without
warning. So, here's a warning.

Since a `direct` url helper block is evaluated using `instance_exec`
then methods that are available in the instance context can be
accessed, e.g. the params object in a controller action or view.

This wasn't clear from the example so expand on that point and add
a test case for this situation.

Better integrate rails-ujs in our repository

We are going to make rails/rails the official repository

Simplify the version specifier generated by prereleases

Further missing requires for Timeout exposed due to Bundler 1.14.5

Bundler 1.14.5 moved to lazily loading 'rubygems/spec_fetcher' which
revealed some missing requires from the JSON encoding test file.

Preload to_datetime before freezing a TimeWithZone instance

remove needless extension from system test example [ci skip]

[doc] Fix wrong class name in testing.md

As the specified command is `rails g system_test articles`, the generated class name
is `ArticlesTest`, not `UsersTest`

Allow 3-level DB configs to group connections by environment

Add CHANGELOG entry for #27384 and #27762

Use double quoted strings, come down hard on some typos.

Implement custom url helpers and polymorphic mapping

[Arthur Nogueira Neves & Matthew Draper]

[ci skip]

The column information for the testings table was being cached
so clear the cache in the test teardown.

[ci skip]

[ci skip]

[ci skip]

For applications that are upgrading or applications that are choosing to
skip system testing Capbyara will not be available. SystemTestCase and
friends shoud only be loaded if Capbyara is defined.

Fixes #28094

Use a separate method called `resolve` for the custom polymorphic
mapping to clarify the API.