test case for #limit added - picking latest value from limit
use `bin/spring` in release notes. [ci skip]

Follow up to: https://github.com/rails/rails/commit/828a8f214535e59d709fd4862605902d1cc21632#commitcomment-4879462

This will be available after https://github.com/jonleighton/spring/commit/c6e25804b3338959d87a29f40967a333c650c031
is released.
MySQL: remove the old-school 'packets out of order' message

Blast from the past, MySQL 4 era, when the password hashing style changed.
Introduce Module#concerning

A natural, low-ceremony way to separate responsibilities within a class.

Imported from https://github.com/37signals/concerning#readme
Merge pull request #13347 from jeremy/concerning

Introduce Module#concerning
minor doc reword. Upgrade Rails itself not to Rails. [ci skip]

/cc @chancancode
Fix indent on AS changelog [ci skip]
release notes link to fixed versions of the API. [ci skip]

As discussed with @fxn the release notes are a snapshot document.
The links going out to the API should represent that exact snapshot.
This means we always link to the full final release. For example
the 3.2 release notes link to http://api.rubyonrails.org/v3.2.0.
Merge pull request #13343 from akshay-vishnoi/test-cases

test case for #limit added - picking latest value from limit
concern doesn't include the module automatically

[ci skip]
Some assorted fixes for the 4.1 release notes:

* Added release notes for secrets.yml and mentioned it in the highlights
* Added release notes for Mailer previews and mentioned it in the highlights
* Added release notes for Module#concerning
* Removed mention for AV extraction from the highlights
* Rearranged the major features to put highlighted features first
* Various improvements and typo fixes

[ci skip]