* Fix indentation.
* Add backticks.

[ci skip] explain async queue and rake tasks

Fixed Frozen string error in actionpack

Remove unneeded `association.respond_to?(:reset_scope)`

CI against JRuby 9.1.9.0

http://jruby.org/2017/05/16/jruby-9-1-9-0

Since 86390c3b all associations have `reset_scope` so `respond_to?` is
unneeded.

Set non 0 value to logger not to be affected by Ruby versions

Address LogSubscriberTest failures to support Rails 2.5.0-dev

Addresses #29021

The object inside the scope is of the class that define the association
not the associated class.

[ci skip]

Added fixed links to code for Rails Guides ActiveSupport

Address #29021

Since Ruby 2.5.0-dev does not return decimal value when it is 0.
This change has been made at Ruby 2.5.0-dev between `(2017-05-05 trunk 58572)`
and `(2017-05-07 trunk 58586)`, likely Revision 58586.

This fix has been tested with these Ruby versions:

* ruby 2.5.0dev (2017-05-15 trunk 58733) [x86_64-linux]
* ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
* ruby 2.3.4p301 (2017-03-30 revision 58214) [x86_64-linux]
* ruby 2.2.7p470 (2017-03-28 revision 58194) [x86_64-linux]

[Yasuo Honda & Ryuta Kamizono]

Fix `TestInvalidUrls` with rack 2.0.3

Respect 'SchemaDumper.ignore_tables' in databases structure dump

* Use NOT IN in SQL query
* Quote table names propertly
* Use array form of command invocation

When using `sql` as the schema format, or even just doing `rake
db:structure:dump`, it would be good to respect the list of ignored
tables that has been configured.

Currently, raise `BadRequest` if params encoding is invalid.
https://github.com/rails/rails/blob/5-1-stable/actionpack/lib/action_dispatch/http/parameters.rb#L64..L74
https://github.com/rails/rails/blob/5-1-stable/actionpack/lib/action_dispatch/request/utils.rb#L26..L39

However, env values are ensure encoded in ASCII 8 BIT at rack 2.0.3.
https://github.com/rack/rack/commit/68db9aa99e3e2775a58621f658b2a7a0f67db459

Therefore, even if specify an invalid urls, it will not cause an error.

Message encryptor auth tag check

Fixes MessageEncryptor when used in AEAD mode. Specifically, we need to check if the `auth_tag` is nil. This may arise when an AEAD encryptor is used to decrypt a ciphertext generated from a different mode, such as CBC-HMAC. Basically, the number of double dashes will differ and `auth_tag` may be nil in this case.

Don't cache locally if unless_exist was passed

When MessageEncryptor tries to +decrypt_and_verify+ ciphertexts
generated in a different mode (such CBC-HMAC), the +auth_tag+ may be
+nil+ and must explicitly check for it.

See the discussion here:
https://github.com/rails/rails/pull/28132#discussion_r116388462

Some cache backends support the `unless_exist` option, which tells them
not to overwrite an existing entry. The local cache currently always
stores the new value, even though the backend may have rejected it.

Since we can't tell which value will end up in the backend cache, we
should delete the key from the local cache, so that the next read for
that key will go to the backend and pick up the correct value.

Previously this implied that system tests provided other non-headless
drivers when Selenium is the only driver that uses `:using`,
`:screen_size` or `:options` arguments.

This change clarifies that Selenium is the only non-headless driver.

It's more likely you'll generate a test for testing users than a users
creates test. This is a better example of a real world test.
Additionally the users create view is unlikely to have the text
"UserCreates" since that is likely generated as well. This is now an
example of visiting the users index.

It wasn't clear that system tests don't run with the rest of the test
suite and are part of a separate command.

This documents the `test:system` command as well as update the Rails
runner help documentation to make it clearer that system tests are run
via their own command by default.

Allow irb options to be passed from `rails console` command

[ci skip] Mailer fixtures in Testing guide.

Update guide to clarify that mailer fixtures are not created when
using the mailer generator.