Issue #2927746 by alexpott, catch, slasher13, mpdonadio, martin107, RoSk0, jibran, larowlan, pounard, Mile23, Jo Fitzgerald, deviantintegral, pritish.kumar: Update Symfony components to 3.4.*

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

Issue #2716685 by Mile23: Part 2: Fix several errors in the 'Drupal.Commenting.DocComment' coding standard

Issue #2572307 by vprocessor, attiks, andriyun, alexpott, pfrenssen: Fix 'Generic.PHP.UpperCaseConstant' coding standard

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #313145 by ghoti, t0xicCode, znerol, pwolanin, thedavidmeister, seanr, neclimdul, Damien Tournoud: Support X-Forwarded-* HTTP headers alternates

Issue #2506533 by Jaesin, minnur, neclimdul, sdstyles, dawehner, Crell: Remove ContentNegotiation and embed functionality in the middleware

Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #2481453 by dawehner, pwolanin, rteijeiro, neclimdul, znerol: Implement query parameter based content negotiation as alternative to extensions

Issue #2368987 by Wim Leers, Berdir, Schnitzel, epari.siva, bircher, vijaycs85, likin: Move internal page caching to a module to avoid relying on config get on runtime

Issue #2286971 by znerol, Berdir, almaudoh, cilefen: Remove dependency of current_user on request and authentication manager

Issue #2229145 by znerol, neclimdul, larowlan, alexpott, joelpittet, almaudoh, tadityar: Register symfony session components in the DIC and inject the session service into the request object

Revert "Issue #2229145 by znerol, neclimdul, larowlan, joelpittet, almaudoh: Register symfony session components in the DIC and inject the session service into the request object"

This reverts commit b926f5d8.

Issue #2229145 by znerol, neclimdul, larowlan, joelpittet, almaudoh: Register symfony session components in the DIC and inject the session service into the request object

Issue #2348679 by znerol, Wim Leers: Move the remaining procedural page cache code to the page cache stack middleware

Issue #2303673 by dawehner, damiankloip, effulgentsia, Fabianx: Implement stackphp; cleanup handlePageCache() and preHandle()