[ticket/13168] Fix mbstring warnings in ACP for PHP 5.6 compatibility

PHPBB3-13168
Merge pull request #3047 from Elsensee/ticket/13168

[ticket/13168] Fix mbstring warnings in ACP for PHP 5.6 compatibility

* Elsensee/ticket/13168:
  [ticket/13168] Fix mbstring warnings in ACP for PHP 5.6 compatibility
[ticket/12120] Remove EXreaction from active authors

PHPBB3-12120
Merge pull request #3051 from nickvergessen/ticket/12120

[ticket/12120] Remove EXreaction from active authors
[ticket/13234] Never allow autologin/remember me to modify the userid

This prevents admin relogin with forced user id from overwriting
remember me cookies

PHPBB3-13234
[ticket/13234] Fix conditions and CS

PHPBB3-13234
Merge pull request #3090 from Nicofuma/ticket/13234

Ticket/13234