[DependencyInjection] added a check for the class name when dumping a container to PHP

src/Symfony/Components/DependencyInjection/Dumper/PhpDumper.php

@@ -87,7 +87,7 @@ EOF;
     {
         $class = $this->dumpValue($definition->getClass());
 
-        if (0 === strpos($class, "'") && !preg_match('/^\'[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*\'$/', $class)) {
+        if (0 === strpos($class, "'") && !preg_match('/^\'[\\a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*\'$/', $class)) {
             throw new \InvalidArgumentException(sprintf('"%s" is not a valid class name.', $class));
         }