Issue #2908079 by jungle, voleger, mpdonadio, zahord, andypost, RoSk0, Mile23,...

Issue #2908079 by jungle, voleger, mpdonadio, zahord, andypost, RoSk0, Mile23, claudiu.cristea, alexpott, xjm, Krzysztof Domański, naveenvalecha, piggito, Suresh Prabhu Parkala, daffie, dawehner, gumanist: Move some of the bootstrap.inc PHP-related constants to \Drupal and deprecate the old versions