Issue #2172235 by joelpittet: Upgrade Twig to 1.15.* from 1.12.*.
Issue #2175769 by alexpott: Fix incorrect variable_del() in update_uninstall().
Issue #2171359 by sun: Output proper exception message for database RowCountExceptions.
Merge branch '8.x' of http://git.drupal.org/project/drupal into 8.x