Merge branch '2.7' into 2.8

* 2.7:
  The exception should be thrown if an object doesn't implement Traversable AND doesn't implement Countable, not when it doesn't implement Traversable but DOES implement Countable
  [Form] fix violation mapper tests
  [HttpKernel] Prevent a fatal error when DebugHandlersListener is used with a kernel with no terminateWithException() method
  don't rely on deprecated YAML parser feature

Author: fabpot

Tests/Dumper/YamlDumperTest.php

@@ -28,14 +28,14 @@ public function testDump()
     {
         $dumper = new YamlDumper($container = new ContainerBuilder());
 
-        $this->assertEqualYamlStructure(self::$fixturesPath.'/yaml/services1.yml', $dumper->dump(), '->dump() dumps an empty container as an empty YAML file');
+        $this->assertEqualYamlStructure(file_get_contents(self::$fixturesPath.'/yaml/services1.yml'), $dumper->dump(), '->dump() dumps an empty container as an empty YAML file');
     }
 
     public function testAddParameters()
     {
         $container = include self::$fixturesPath.'/containers/container8.php';
         $dumper = new YamlDumper($container);
-        $this->assertEqualYamlStructure(self::$fixturesPath.'/yaml/services8.yml', $dumper->dump(), '->dump() dumps parameters');
+        $this->assertEqualYamlStructure(file_get_contents(self::$fixturesPath.'/yaml/services8.yml'), $dumper->dump(), '->dump() dumps parameters');
     }
 
     /**