Issue #1987848 by disasm, ocsilalala, kim.pepper, pwieck, Cottser, pratik60, h3rj4n, pfrenssen, InternetDevels, ParisLiakos, rgoodine, tlyngej, vijaycs85, robeano: Convert system_theme_default() to a new style controller.
Issue #2233403 by Jalandhar, sun: Let update.php invoke hooks again.
Revert Issue #421294: We use unicode, not html entities.