Update sites improvements && Improvements for updates, per the comments in gh-5296.

siehe: https://github.com/joomla/joomla-cms/commit/4fe493d54f086b2199889da70bdf97df5beb511a und https://github.com/joomla/joomla-cms/commit/673effa2c1bb25c666f5889e86f57e67fff07bdc