Make all WATCHers dirty when the slave reloads the DB.
fix comments forgotten in #285 (zipmap -> ziplist)
Sentinel: advertise the promoted slave address only after successful setup.
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.
Makefile: valgrind target added (forces -O0 and libc malloc).
Redis 2.6.10
Format to fit 80 columns

This makes it readable on GitHub and editors without auto wrapping.
Test: avoid false positives in CLIENT SETNAME closed connection test.
Replication: more strict error checking for master PING reply.