Merge branch '3.1'

* 3.1:
  fixed bad merge
  Fix PHP 7.1 related failures
  [VarDumper] Fix for 7.1
  fixed CS
  Added class existence check if is_subclass_of() fails in compiler passes
  Fix the DBAL session handler version check for Postgresql

Author: fabpot

Tests/CrossCheckTest.php

@@ -34,7 +34,7 @@ public function testCrossCheck($fixture, $type)
         $loaderClass = 'Symfony\\Component\\DependencyInjection\\Loader\\'.ucfirst($type).'FileLoader';
         $dumperClass = 'Symfony\\Component\\DependencyInjection\\Dumper\\'.ucfirst($type).'Dumper';
 
-        $tmp = tempnam('sf_service_container', 'sf');
+        $tmp = tempnam(sys_get_temp_dir(), 'sf');
 
         file_put_contents($tmp, file_get_contents(self::$fixturesPath.'/'.$type.'/'.$fixture));