Removing redundant 'happens' in callbacks documentation

`md5` --> `MD5`

Sorry, I missed a few places in my last PR. This should be the last of
'em 😬

update to make it less obvious that this guide is from 2008/2009

Using locals will cause layouts to be cached multiple times in the
template cache.  This commit removes locals from consideration when
looking up the layout.

* Update documentation about Safari 4 supporting http only cookie

- Source: www.greebo.net/2009/06/09/httponly-in-safari-40-release/ via http://stackoverflow.com/questions/528405/which-browsers-do-support-httponly-cookies

Fix security guide capitalization errors

malicious ads are neither new nor unusual
live HTTP headers project is dead - see https://www.mozdev.org/bugs/show_bug.cgi?id=25944

Add Attributes API to release notes [ci skip]

Would have submitted to docrails, but this guide was just changed today,
and docrails doesn't have the most updated version 😬

cc @vipulnsward

[ci skip]

`md5` --> `MD5`

Update the Rails security guide [ci skip]

[ci skip]

Leftover from an earlier commit, chose to fix because I was
just down in this file.

Per request digest caches were added before we had hooks into
different units of work that Rails performs.

As such the most reliable way to prevent stale cache digests
was with a middleware. The middleware prevented staleness in
Action Controller requests.

However, the executor is superior because it should also prevent
staleness when running just Active Job jobs or broadcasting
through Action Cable's server.

Bring up-to-date the information about the session id in the
Sessions section. The guide currently says that the session
id is a md5 hash while the implementation uses a random hex
string.

Fixes #25032.

[ci skip]

Forward ActiveRecord::Relation#count to Enumerable#count if block given

Introduce Date#all_day

Keep previous state around for nested calls to #suppress

If a call to #suppress from the same class occurred inside another #suppress
block, the suppression state would be set to false before the outer block
completes.

This change keeps the previous state around in memory and unwinds it
as the blocks exit.

Fix bug in JSON deserialization when column default is an empty string

Rails 5.1 point type should not raise exception if empty string is provided as input

Follows the same pattern as controllers and jobs. Exceptions raised in
delivery jobs (enqueued by `#deliver_later`) are also delegated to the
mailer's rescue_from handlers, so you can handle the DeserializationError
raised by delivery jobs:

```ruby
class MyMailer < ApplicationMailer
  rescue_from ActiveJob::DeserializationError do
    …
  end
```

ActiveSupport::Rescuable polish:
* Add the `rescue_with_handler` class method so exceptions may be
  handled at the class level without requiring an instance.
* Rationalize `exception.cause` handling. If no handler matches the
  exception, fall back to the handler that matches its cause.
* Handle exceptions raised elsewhere. Pass `object: …` to execute
  the `rescue_from` handler (e.g. a method call or a block to
  instance_exec) against a different object. Defaults to `self`.

Add some assertions for BigDecimal#to_s

Conventionally envs are ordered development -> test -> production.

Add Action Cable guide to list

Document and test ActionDispatch server_port

Conflicts:
	guides/source/configuring.md

Perfomance fix for ActiveSupport Enumerable#index_by

Calculating -------------------------------------
              before    34.731k i/100ms
               after    48.206k i/100ms
-------------------------------------------------
              before    508.451k (± 1.2%) i/s -      2.570M
               after    720.068k (± 0.9%) i/s -      3.615M
Comparison:
               after:   720067.6 i/s
              before:   508451.1 i/s - 1.42x slower

Add missing space and newline for clarity

Add notes on cosmetic patches to contributing guidelines

Add output snippet from `ActionController::API.ancestors - ActionController::Metal.ancestors` command for api apps.
[ci skip]