Issue #2867757 by alexpott, Mile23, anavarre, David_Rothstein, cilefen, kylebrowning, xjm: Improve instructions for updating composer.json and /vendor

(cherry picked from commit 5cff356c)

Issue #2701541 by xjm, yoroy, catch, mikeryan, Gábor Hojtsy: Rename Drupal Upgrade UI to Migrate Drupal UI

Issue #2701027 by Gábor Hojtsy: Drupal 8 UPGRADE.txt is misleading in many ways (in its name to begin with)

Issue #2599190 by chegor, rakesh.gectcr, sdstyles, aneeshthankachan, anil280988, Himanshu5050, jhodgdon: Update upgrading procedure describing in UPGRADE.txt

Issue #2562581 by mikeryan, a_thakur, jhodgdon, phenaproxima, cilefen, ultimike: Update UPGRADE.txt for RC

Issue #2516842 by er.pushpinderrana, thejacer87, jhodgdon: UPGRADE.txt should explain where to find release notes

Issue #2507911 by mikebell_, dylanf, naveenvalecha, deepakaryan1988, kfitz, jhodgdon, webchick, Charles Belov: Mention location of settings.php in UPGRADE.txt

Issue #2491155 by mikeburrelljr, Mac_Weber, opdavies: Update drupal.org and kernel.org URLs in core modules (Follow-up to 2489912)

Issue #1975220 by davidwbarratt, tstoeckler, mradcliffe, RobLoach, Mile23, hussainweb: Allow a Composer user to manage Drupal, modules, and PHP dependencies with a custom root composer.json

Issue #1817020 by paulh: Remove information about using upgrade.php to do major version upgrades from UPGRADE.txt

- Patch #1167996 by rocket_nova, Sheldon Rampton: UPGRADE.txt needs to say all D6 contrib modules need to be upgraded to their latest D6 versions before the D6->D7 update.

Nate Lampton authored Oct 30, 2011 and catch committed Nov 01, 2011

Issue #22336 by quicksketch, scor, boombatower, and rfay. Move all core Drupal files under a core subdirectory.

Nate Lampton authored Oct 30, 2011 and catch committed Nov 01, 2011

Issue #22336 by quicksketch, scor, boombatower, and rfay. Move all core Drupal files under a core subdirectory.

Issue #1040810 by Tor Arne Thune: Fixed UPGRADE.txt describes erroneous step and should mention release notes.

- Patch #1029346 by David_Rothstein: Changed INSTALL.txt and UPGRADE.txt should mention that you can download Drupal as a .zip file also.

- Patch #295255 by yettyn, jhodgdon, sun, effulgentsia, nirbhasa: clean-up the upgrade path: UPGRADE.txt.

- Patch #865072 by bleen18, jhodgdon: Bartik is default theme now ... documentation & tests need to be changed.

#450540 by mcrittenden: Remove reference to Stark in upgrade documentation, since it only appears in D7.

#67234 by Ralf, Dave Reid, David_Rothstein, Rob Loach, dww, et al: Added a permission to update.php.

- Patch #570572 by winston, David_Rothstein | Shai, Xano, alexanderpas, emmajane, kazar: changed label for user/1 account from 'administrator' to 'site maintenance account'.

- Patch #430342 by kkaefer et al: usability improvement: changed 'site maintenance' to 'maintenance mode'.

#206281 by keith.smith: document that people should look into the new system requirements when they upgrade

#175876 by hazexp, webernet, keith.smith: unify module/theme/translation download links and include more pointers to these locations