Merge branch '3.1'

* 3.1:
  [FrameworkBundle] Check for class existence before is_subclass_of
  Update GroupSequence.php
  Code enhancement and cleanup
  [Form] Fix transformer tests after the ICU update
  [DI] Add anti-regression test
  Revert "minor #19689 [DI] Cleanup array_key_exists (ro0NL)"
  bumped Symfony version to 3.1.5
  updated VERSION for 3.1.4
  updated CHANGELOG for 3.1.4
  bumped Symfony version to 2.8.11
  updated VERSION for 2.8.10
  updated CHANGELOG for 2.8.10
  [BrowserKit] Fix cookie expiration on 32 bit systems
  bumped Symfony version to 2.7.18
  updated VERSION for 2.7.17
  update CONTRIBUTORS for 2.7.17
  updated CHANGELOG for 2.7.17
  Update misleading comment about RFC4627

Author: nicolas-grekas

Command/YamlLintCommand.php

@@ -29,7 +29,7 @@ protected function configure()
         parent::configure();
 
         $this->setHelp(
-                $this->getHelp().<<<EOF
+            $this->getHelp().<<<EOF
 
 Or find all files in a bundle:
 

DependencyInjection/Compiler/AddConsoleCommandPass.php

@@ -35,6 +35,10 @@ public function process(ContainerBuilder $container)
 
             $class = $container->getParameterBag()->resolveValue($definition->getClass());
             if (!is_subclass_of($class, 'Symfony\\Component\\Console\\Command\\Command')) {
+                if (!class_exists($class, false)) {
+                    throw new \InvalidArgumentException(sprintf('Class "%s" used for service "%s" cannot be found.', $class, $id));
+                }
+
                 throw new \InvalidArgumentException(sprintf('The service "%s" tagged "console.command" must be a subclass of "Symfony\\Component\\Console\\Command\\Command".', $id));
             }
             $container->setAlias($serviceId = 'console.command.'.strtolower(str_replace('\\', '_', $class)), $id);