Expiration time is a 32-bit value as specified by memcached protocol.
Thus, no need to store it as a 64-bit value. When the value is needed,
convert it to the target type. Change intended to save space from
item structure.
In addition, there is no need to insert an entry into _alive when
expiration time is zero, meaning item will never expire.
Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
66117b2697