Enable to skip sending reconfirmation email when skip_confirmation_notification! is invoked

We could always generate a confirmation token but not sending a
confirmation email by invoking the skip_confirmation_notification!
method when creating the account.
But there were no way to do that when we were turning on reconfirmable
and updating email.
Fix improper login param sanitization permit

This includes a failing test case that hooks into ActiveSupport
Notifications to catch the param permit error.
Add thread-safety support note
CHANGELOG fix about _links.erb partial revert

9bf718 got reverted by aa2d15 but the CHANGELOG was not reflected to
show this.
Merge pull request #2485 from betelgeuse/changelog_fix

CHANGELOG fix about _links.erb partial revert
Merge pull request #2475 from tkhr/enable_skipping_reconfirmation_notification_but_regenerate_confirmation_token_2

Enable to skip sending reconfirmation email when reconfirmable is on and skip_confirmation_notification! is invoked
Merge pull request #2419 from plataformatec/issue-2418

set error to the field specified in unlock_keys config
Merge pull request #2452 from latortuga/bad-strong-params-on-failed-login

Add failing test case for bad parameter sanitizing when failing to login
Update CHANGELOG
Use Rails 4.0.0 final