Issue #1798732 by Dean Reilly, westie, alexpott, sun: convert install_task() variable to use state system.

Issue #1723892 by Berdir, Pancho, das-peter, fago: Support for revisions for entity save and delete operations.

Issue #1808864 by fastangel, Jose Reyero: Fixed Exception handling is not 'locale safe' (thus not database safe).

Issue #1798732 by Dean Reilly, westie, alexpott: Convert install_task() variable to use state system.

Issue #1802072 by fubhy, Stalski: Ajax callbacks should be callbacks defined as function or class method.

Issue #1809962 by Jose Reyero, sun: Move some locale updates to update.inc for a safe language upgrade.

Issue #1788462 by samhassell: Remove references to 'active store' in comments for configuration system.

Issue #1608842 by chx, alexpott, sun, effulgentsia, beejeebus, tim.plunkett et al: Replace list of bootstrap modules, enabled modules, enabled themes, and default theme with config.

Issue #1620114 by Rob Loach, sun: Explicitly register \Drupal\Component and \Drupal\Core to increase class lookup performance.

Issue #1642526 by andypost, Berdir, dixon_: Add upgrade path from for generating UUIDs for all core entities.

Issue #742344 by sun, pillarsdotnet, tarmstrong, neilnz, wamilton, lucascaro: Allow forms to set custom validation error messages on required fields.

Issue #1742438 by larowlan, Christian Biggins, kim.pepper, Everett Zufelt: Fixed Vertical tabs header and container rendered even when no vertical tabs.

Issue #1760530 by jenlampton, Albert Volkman, crazyrohila, Risse, justafish, Fabianx: Move all template files provided by core modules and themes into a 'templates' directory inside that module directory.

Issue #1326664 by Lars Toomre, Albert Volkman, sven.lauer, tim.plunkett: API docs cleanup for parts of system module and other files

Issue #1608878 by jessebeach, tim.plunkett, dead_arm, nod_, sun, effulgentsia, Everett Zufelt, geerlingguy: Added CTools dropbutton to core.

Issue #1393392 by c960657, fubhy: Convert prefix cache clears to cache tags, then remove support for them.