authmemcookie: Set expiry time of session data when saving to memcache.
authmemcookie: Set expiry time of session data when saving to memcache.

Patch by Ernesto Revilla.

Rud5G/simplesamlphp,Rud5G/simplesamlphp,Rud5G/simplesamlphp,Rud5G/simplesamlphp