[ticket/11700] Fix extension loading with namespaces

class loader now expects all classes to be prefixed with a backslash
when resolving paths

PHPBB3-11700

tests/extension/ext/foo/acp/fail_info.php

@@ -11,7 +11,7 @@ class foo_info
 	public function module()
 	{
 		return array(
-			'filename'	=> 'phpbb_ext_foo_acp_fail_module',
+			'filename'	=> 'foo\acp\fail_module',
 			'title'		=> 'Foobar',
 			'version'	=> '3.1.0-dev',
 			'modes'		=> array(