bug 451 fixed: problem with auto login

- add an auto_login_key in users_table
- $conf['session_length'] is no more useful 
    and sessions length will be 0 (until browser closed)
- add $conf['remember_me_name'] for cookie remember name


git-svn-id: http://piwigo.org/svn/trunk@1493 68402e56-0260-453c-a942-63ccdbb3a9ee

install/phpwebgallery_structure.sql

@@ -1,4 +1,4 @@
--- MySQL dump 9.11
+1-- MySQL dump 9.11
 --
 -- Host: localhost    Database: pwg-bsf
 -- ------------------------------------------------------
@@ -345,6 +345,7 @@ CREATE TABLE `phpwebgallery_users` (
   `username` varchar(20) binary NOT NULL default '',
   `password` varchar(32) default NULL,
   `mail_address` varchar(255) default NULL,
+  `auto_login_key` varchar(64) default NULL,
   PRIMARY KEY  (`id`),
   UNIQUE KEY `users_ui1` (`username`)
 ) TYPE=MyISAM;