Issue #2406681 by tstoeckler, hussainweb, alexpott, ParisLiakos, almaudoh, tadityar: Add an autoload.php in the repo root to control the autoloader of front controllers

Issue #2304949 by mpdonadio, cilefen, znerol, klausi, gaurav.goyal, regilero: Port HTTP Host header DoS fix from SA-CORE-2014-003

Issue #2328111 by dawehner, martin107, neclimdul: Replace most instances of the DRUPAL_ROOT constant with the app.root container parameter.

Issue #2016629 by larowlan, neclimdul, sun, alexpott, jibran, ParisLiakos, donquixote, effulgentsia, msonnabaum: Refactor bootstrap to better utilize the kernel.

Revert "Issue #2016629 by larowlan, neclimdul, sun, alexpott, jibran, ParisLiakos, donquixote, effulgentsia, msonnabaum: Refactor bootstrap to better utilize the kernel."

This reverts commit cda051c4.

Issue #2016629 by larowlan, neclimdul, sun, alexpott, jibran, ParisLiakos, donquixote, effulgentsia, msonnabaum: Refactor bootstrap to better utilize the kernel.