Merge branch '2.6' into 2.7

* 2.6:
  [Security] fix check for empty usernames
  [Form] updated exception message of ButtonBuilder::setRequestHandler()
  [travis] Fix deps=high jobs
  [HttpFoundation] [PSR-7] Allow to use resources as content body and to return resources from string content
  [DependencyInjection] Remove unused code in XmlFileLoader
  [HttpFoundation] Behaviour change in PHP7 for substr
  bumped Symfony version to 2.3.32
  updated VERSION for 2.3.31
  update CONTRIBUTORS for 2.3.31
  updated CHANGELOG for 2.3.31

Conflicts:
	src/Symfony/Bridge/Twig/composer.json
	src/Symfony/Bundle/FrameworkBundle/composer.json

Author: nicolas-grekas

Loader/XmlFileLoader.php

@@ -49,7 +49,7 @@ public function load($resource, $type = null)
         $this->parseImports($xml, $path);
 
         // parameters
-        $this->parseParameters($xml, $path);
+        $this->parseParameters($xml);
 
         // extensions
         $this->loadFromExtensions($xml);
@@ -70,9 +70,8 @@ public function supports($resource, $type = null)
      * Parses parameters.
      *
      * @param \DOMDocument $xml
-     * @param string       $file
      */
-    private function parseParameters(\DOMDocument $xml, $file)
+    private function parseParameters(\DOMDocument $xml)
     {
         if ($parameters = $this->getChildren($xml->documentElement, 'parameters')) {
             $this->container->getParameterBag()->add($this->getArgumentsAsPhp($parameters[0], 'parameter'));