[ticket/14733] Make sure detect_algorithm() works correctly and add tests

detect_algorithm() returned array() if an algorithm prefix was more than 2
characters long. This might have been invalid for other prefixes. In order
to correctly cope with other prefixes, another check for a backslash in the
prefix definitino has been added.
This was discovered while writing the tests for the newly added interface.

PHPBB3-14733

phpBB/phpbb/passwords/manager.php

@@ -174,7 +174,7 @@ class manager
 
 		// Be on the lookout for multiple hashing algorithms
 		// 2 is correct: H\2a > 2, H\P > 2
-		if (strlen($match[1]) > 2)
+		if (strlen($match[1]) > 2 && strpos($match[1], '\\') !== false)
 		{
 			$hash_types = explode('\\', $match[1]);
 			$return_ary = array();