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
CSRF protection from cross-origin <script> tags

Thanks to @homakov for sounding the alarm about JSONP-style data leaking