merge r25633 from trunk to branch 2.5

Small bug on password hash verification with strpos function

git-svn-id: http://piwigo.org/svn/branches/2.5@25634 68402e56-0260-453c-a942-63ccdbb3a9ee

include/functions_user.inc.php

@@ -1171,7 +1171,7 @@ function pwg_password_verify($password, $hash, $user_id=null)
   global $conf, $pwg_hasher;
 
   // If the password has not been hashed with the current algorithm.
-  if (strpos('$P', $hash) !== 0)
+  if (strpos($hash, '$P') !== 0)
   {
     if (!empty($conf['pass_convert']))
     {