Now we keep only the common code and move the specific code to the gems

use self instead of #read_attribute

Fix for configuring rails guide [ci skip]

`ActiveSupport::Logger` has no concept like auto flushing since it has no userspace buffering.
It's a remnant of `ActiveSupport::BufferedLogger` epoch which was since removed from rails.

Allow polymorphic routes with nil when a route can still be drawn

Clarify that /console is an optional feature

(/console is not mounted by default with web-console 2.0.)

Suppose you have two resources routed in the following manner:

```ruby
resources :blogs do
  resources :posts
end

resources :posts
```

When using polymorphic resource routing like `url_for([@blog, @post])`, and `@blog` is `nil` Rails should still try to match the route to the top-level posts resource.

Fixes #16754

[ActionMailer] Rename test/test_test to test/test_case_test

[ci skip] add line about text layout

Sets the connection collation to the database collation configured
in database.yml. Otherwise, `SET NAMES utf8mb4` will use the default
collation for that charset (utf8mb4_general_ci) when you may have chosen
a different collation, like utf8mb4_unicode_ci.

This only applies to literal string comparisons, not column values, so
it is unlikely to affect you.

so this assertion causes random test fail

When we are loading a component and we want to know its version, we are
actually not speaking about the constant but the library itself.

[ci skip]

[Godfrey Chan & Xavier Noria]

Use system /tmp for temp files when testing actionpack

This was removed by mistake in 5e51bdda

`try` allocates an array on every call, we should avoid calling it in
hotspots.  This reduced AttributeMethodsTest#test_setting_time_zone_aware_attribute_with_string
from 18k allocations to 14k

We tenderized the wrong method! Object#try already had the yield option, just needed some tenderloving instance_eval to fit the bill

Fixed Active Job Backburner adapter

This fixes random test failure in migrator_test.rb

Make test:isolated run without bundler for Action Mailer

Avoid skipping Sidekiq tests on Rubinius

Now that Travis provides support for Rubinius 2.2.10, we can run the
Sidekiq tests against this version.