Allow administrators to define custom session handlers for SquirrelMail without needing to change anything in php.ini (application-level).

In config_local.php, admin needs to put:

$custom_session_handlers = array( 'my_open_handler', 'my_close_handler', 'my_read_handler', 'my_write_handler', 'my_destroy_handler', 'my_gc_handler', ); session_module_name('user'); session_set_save_handler( $custom_session_handlers[0], $custom_session_handlers[1], $custom_session_handlers[2], $custom_session_handlers[3], $custom_session_handlers[4], $custom_session_handlers[5] );

We need to replicate that code once here because PHP has long had a bug that resets the session handler mechanism when the session data is also destroyed. Because of this bug, even administrators who define custom session handlers via a PHP pre-load defined in php.ini (auto_prepend_file) will still need to define the $custom_session_handlers array in config_local.php.