Merge branch '2.3' into 2.6

* 2.3:
  Remove some useless @group annotations
  Removed useless strtolower call
  [Validator] Use strict comparisons in loaders
  CS: Use "self" keyword instead of class name if possible

ContainerBuilder.php

@@ -768,7 +768,7 @@ public function getAlias($id)
      */
     public function register($id, $class = null)
     {
-        return $this->setDefinition(strtolower($id), new Definition($class));
+        return $this->setDefinition($id, new Definition($class));
     }
 
     /**