[FrameworkBundle] Allow custom services for validator mapping cache.

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php

@@ -442,7 +442,12 @@ class Configuration implements ConfigurationInterface
                     ->info('validation configuration')
                     ->canBeEnabled()
                     ->children()
-                        ->scalarNode('cache')->end()
+                        ->scalarNode('cache')
+                            ->beforeNormalization()
+                                // Can be removed in 3.0, once ApcCache support is dropped
+                                ->ifString()->then(function ($v) { return 'apc' === $v ? 'validator.mapping.cache.apc' : $v; })
+                            ->end()
+                        ->end()
                         ->booleanNode('enable_annotations')->defaultFalse()->end()
                         ->arrayNode('static_method')
                             ->defaultValue(array('loadValidatorMetadata'))

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php

@@ -716,7 +716,7 @@ class FrameworkExtension extends Extension
                 'validator_'.hash('sha256', $container->getParameter('kernel.root_dir'))
             );
 
-            $validatorBuilder->addMethodCall('setMetadataCache', array(new Reference('validator.mapping.cache.'.$config['cache'])));
+            $validatorBuilder->addMethodCall('setMetadataCache', array(new Reference($config['cache'])));
         }
 
         switch ($config['api']) {