Merge branch '2.8' into 3.1

* 2.8:
  [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 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

@@ -82,7 +82,6 @@ protected function execute(InputInterface $input, OutputInterface $output)
             throw new \RuntimeException(sprintf('File or directory "%s" is not readable', $filename));
         }
 
-        $files = array();
         if (is_file($filename)) {
             $files = array($filename);
         } elseif (is_dir($filename)) {

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);