fix container cache key generation

If the actual class name were not taken into, we would not be able to
detect inconsistencies between the different configuration formats (PHP,
YAML, and XML) as the container built based on the first evaluated
configuration format would be cached and reused by tests for the other
formats too.

Author: xabbuh

Tests/DependencyInjection/FrameworkExtensionTest.php

@@ -309,7 +309,7 @@ protected function createContainer(array $data = array())
 
     protected function createContainerFromFile($file, $data = array())
     {
-        $cacheKey = md5($file.serialize($data));
+        $cacheKey = md5(get_class($this).$file.serialize($data));
         if (isset(self::$containerCache[$cacheKey])) {
             return self::$containerCache[$cacheKey];
         }