LASTSAVE is a "random" command.
Make all WATCHers dirty when the slave reloads the DB.
Add SO_KEEPALIVE support to anet.c.
Set SO_KEEPALIVE on client sockets if configured to do so.
tcp-keepalive option documented in redis.conf.
Tcp keep-alive: send three probes before detectin an error.

Otherwise we end with less reliable connections because it's too easy
that a single packet gets lost.
TCP keep-alive. Better documentation in redis.conf.