Merge branch '2.8' into 3.0

* 2.8:
  [Finder] Partially revert #17134 to fix a regression
  [HttpKernel] Fix mem usage when stripping the prod container
  exception when registering bags for started sessions

Conflicts:
	src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php
	src/Symfony/Component/Validator/composer.json

Author: nicolas-grekas

Kernel.php

@@ -629,10 +629,7 @@ protected function dumpContainer(ConfigCache $cache, ContainerBuilder $container
             $dumper->setProxyDumper(new ProxyDumper(md5($cache->getPath())));
         }
 
-        $content = $dumper->dump(array('class' => $class, 'base_class' => $baseClass, 'file' => $cache->getPath()));
-        if (!$this->debug) {
-            $content = static::stripComments($content);
-        }
+        $content = $dumper->dump(array('class' => $class, 'base_class' => $baseClass, 'file' => $cache->getPath(), 'debug' => $this->debug));
 
         $cache->write($content, $container->getResources());
     }