This modification mostly follows the principles of Dan Wheelers password strength estimator zxcvbn. It does not weight password strength by their combination of upper/lower letters, special characters and numbers, but on how easy they are to crack in reality.
Fix changing user entity while a write is pending in some cases
Add "Use rejected password fragments in password meter" option (default disabled).
Take rejected password fragments into consideration when showing the password strength meter to the user. Security note: this makes the full list of rejected password fragments visible to end users; ensure that there aren't any sensitive password fragments before enabling.