Revert "Issue #2712647 by klausi, catch, slasher13, jibran, Manuel Garcia, alexpott, naveenvalecha, neclimdul, dawehner, Wim Leers, pounard: Update Symfony components to ~3.1"

This reverts commit a55b8ef1.

Issue #2712647 by klausi, catch, slasher13, jibran, Manuel Garcia, alexpott, naveenvalecha, neclimdul, dawehner, Wim Leers, pounard: Update Symfony components to ~3.1

Issue #2808085 by klausi, claudiu.cristea, stof, nicolas.grekas: Pipe char in locators break Mink and Symfony element search

Issue #2763787 by pwolanin, nerdstein, rlhawk, YesCT, slasher13, tuutti, alexpott, therealssj, TravisCarden, dawehner, maximpodorov, klausi, catch, talhaparacha, Eric_A: Upgrade random_compat to latest version

Revert "Issue #2763787 by nerdstein, rlhawk, slasher13, therealssj, TravisCarden: Upgrade random_compat to latest version"

This reverts commit 7feb65ba.

Issue #2763787 by nerdstein, rlhawk, slasher13, therealssj, TravisCarden: Upgrade random_compat to latest version

Issue #1869548 by dawehner, jeqq, dmouse, slasher13, damiankloip, alexpott, nod_, AlxVallejo, chr.fritsch, yanniboi, effulgentsia, dixon_, -enzo-, Wim Leers, Crell, andypost, catch, Damien Tournoud, kim.pepper, linclark: Opt-in CORS support

Revert "Issue #1869548 by dawehner, jeqq, dmouse, damiankloip, nod_, AlxVallejo, chr.fritsch, yanniboi, effulgentsia, dixon_, -enzo-, Wim Leers, Crell, Damien Tournoud, andypost, kim.pepper, linclark, catch: Opt-in CORS support"

This reverts commit f2b71152.

Issue #1869548 by dawehner, jeqq, dmouse, damiankloip, nod_, AlxVallejo, chr.fritsch, yanniboi, effulgentsia, dixon_, -enzo-, Wim Leers, Crell, Damien Tournoud, andypost, kim.pepper, linclark, catch: Opt-in CORS support

SA-CORE-2016-003 by alexpott, Michael Dowling, mlhess, xjm, Pere Orga, dawehner, greggles, coltrane, pwolanin, larowlan

Issue #2712637 by klausi, jibran, dawehner, simensen, JeroenT: Update stack/builder for Symfony 3 compatibility

Issue #2638856 by bojanz, webflo, SiliconMind: Unable to install modules with core dependencies via composer

Issue #2678574 by dawehner: Symfony 2.8 requirements change: required PHP "iconv" extension is nowhere documented

Issue #2550519 by klausi, nullkernel, cweagans, alexpott, pwolanin, neclimdul: Crypt::randomBytes() doesn't actually return cryptographically secure random bytes

Issue #2600176 by alexpott, dawehner, tim.plunkett: Step 1.875: Include the PhantomJS Mink driver for real

Issue #2380389 by webflo, Mile23, davidwbarratt, timmillwood, hussainweb, tstoeckler, bojanz, yched, MKorostoff, alexpott, webchick: Use a single vendor directory in the root

Issue #2571817 by Cottser, hussainweb: Remove race condition handling in TwigEnvironment::loadTemplate(), it's fixed upstream now

Issue #2568171 by Cottser, dawehner, hussainweb, Wim Leers, cilefen, znerol: Upgrade to Twig 1.22 and implement our own cache class

Issue #2568085 by plach, alexpott, dawehner, Berdir: Lock Twig on ~1.21.2 until we are able to upgrade to 1.22.0