[FrameworkBundle] Fix unintuitive merging behavior for assets_base_urls

See: 4061114562acb7a84b1d368898dac40b719b77b0

Author: jmikola

DependencyInjection/Configuration.php

@@ -226,6 +226,7 @@ private function addTemplatingSection(ArrayNodeDefinition $rootNode)
                     ->fixXmlConfig('assets_base_url')
                     ->children()
                         ->arrayNode('assets_base_urls')
+                            ->performNoDeepMerging()
                             ->addDefaultsIfNotSet()
                             ->defaultValue(array('http' => array(), 'ssl' => array()))
                             ->beforeNormalization()