Merge branch '2.3' into 2.4

* 2.3:
  bumped Symfony version to 2.3.18
  updated VERSION for 2.3.17
  update CONTRIBUTORS for 2.3.17
  updated CHANGELOG for 2.3.17
  added XSD to PHPUnit configuration
  bug #11319 [HttpKernel] Ensure the storage exists before purging it in ProfilerTest
  [Translation] Added unescaping of ids in PoFileLoader
  updated italian translation for validation messages
  [DomCrawler] Fix docblocks and formatting.
  [DomCrawler] Remove the query string and the anchor of the uri of a link
  Simplified the Travis test command
  [Console] Make sure formatter is the same

Conflicts:
	src/Symfony/Component/HttpKernel/Kernel.php

phpunit.xml.dist

@@ -1,6 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit backupGlobals="false"
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.1/phpunit.xsd"
+         backupGlobals="false"
          backupStaticAttributes="false"
          colors="true"
          convertErrorsToExceptions="true"
@@ -8,7 +10,6 @@
          convertWarningsToExceptions="true"
          processIsolation="false"
          stopOnFailure="false"
-         syntaxCheck="false"
          bootstrap="vendor/autoload.php"
 >
     <testsuites>