Description:
------------
The session system always specify expiration by timestamp.
This is ok but it can lead to premature session expiration if the web server and the memcache server do not share the same clock and are out of sync.
I suggest to switch to relative mode and only use absolute mode when session.gc_maxlifetime is greater than 30 days.

see https://github.com/memcached/memcached/blob/master/doc/protocol.txt







Test script:
---------------
file php_memcached.c : line 2526

    if (sess_lifetime > 0) {
        expiration = time(NULL) + sess_lifetime;
    } else {
        expiration = 0;
    }

can be

    if (sess_lifetime > 0) {
        expiration = sess_lifetime;
        if (sess_lifetime >= 2592000) expiration += time(NULL);
    } else {
        expiration = 0;
    }