Merge branch '2.8' into 3.0

* 2.8:
  [travis] timeout the sigchild tests at 60s
  CS: Single line comments should use double slashes (//) and not hash (#).
  Do not use HttpKernel Extension when not needed for 2.7
  Do not use HttpKernel Extension when not needed
  bumped Symfony version to 2.8.2
  updated VERSION for 2.8.1
  updated CHANGELOG for 2.8.1
  bumped Symfony version to 2.7.9
  updated VERSION for 2.7.8
  updated CHANGELOG for 2.7.8
  bumped Symfony version to 2.3.37
  updated VERSION for 2.3.36
  update CONTRIBUTORS for 2.3.36
  updated CHANGELOG for 2.3.36
  Revert "Revert "bug #17052 [2.7] Fixed flatten exception recursion with errors (GrahamCampbell)""
  Revert "bug #17052 [2.7] Fixed flatten exception recursion with errors (GrahamCampbell)"
  use nowdoc instead of heredoc

Conflicts:
	CHANGELOG-2.3.md
	CHANGELOG-2.7.md
	CHANGELOG-2.8.md
	src/Symfony/Bundle/FrameworkBundle/Command/RouterApacheDumperCommand.php
	src/Symfony/Bundle/WebProfilerBundle/Command/ExportCommand.php
	src/Symfony/Bundle/WebProfilerBundle/Command/ImportCommand.php
	src/Symfony/Component/Console/Shell.php
	src/Symfony/Component/Console/Tests/Helper/LegacyTableHelperTest.php
	src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php
	src/Symfony/Component/HttpKernel/Kernel.php

Author: nicolas-grekas

Tests/Definition/Dumper/YamlReferenceDumperTest.php

@@ -28,7 +28,7 @@ public function testDumper()
 
     private function getConfigurationAsString()
     {
-        return <<<EOL
+        return <<<'EOL'
 acme_root:
     boolean:              true
     scalar_empty:         ~