Merge branch '2.8' into 3.1

* 2.8:
  [TwigBundle] fixed usage of getSource in tests
  Trim constant values in XmlFileLoader
  move test to the HttpKernel component
  [TwigBridge] fixed Twig_Source required argument

Author: fabpot

Loader/XmlFileLoader.php

@@ -391,7 +391,7 @@ private function getArgumentsAsPhp(\DOMElement $node, $name, $lowercase = true)
                     $arguments[$key] = $arg->nodeValue;
                     break;
                 case 'constant':
-                    $arguments[$key] = constant($arg->nodeValue);
+                    $arguments[$key] = constant(trim($arg->nodeValue));
                     break;
                 default:
                     $arguments[$key] = XmlUtils::phpize($arg->nodeValue);