Fix a bug in srandmemberWithCountCommand()

In CASE 2, the call sunionDiffGenericCommand will involve the string "srandmember"
> sadd foo one
(integer 1)
> sadd srandmember two
(integer 2)
> srandmember foo 3
1)"one"
2)"two"
Fix a few typos and improve grammar of redis.conf

Make several edits to the example redis.conf configuration file for
improved flow and grammar.

Signed-off-by: David Celis <me@davidcel.is>
retval doesn't initalized

If each if conditions are all fail, variable retval will under uninitlized
Check available tcl versions
Enforce tcl 8.5 or newer
Use `info nameofexectuable`  to find current executable
Test: No clients timeout while testing.
Turn off TCP_NODELAY on the slave socket after SYNC.

Further details from @antirez:

It was reported by @StopForumSpam on Twitter that the Redis replication
link was strangely using multiple TCP packets for multiple commands.
This wastes a lot of bandwidth and is due to the TCP_NODELAY option we
enable on the socket after accepting a new connection.

However the master -> slave channel is a one-way channel since Redis
replication is asynchronous, so there is no point in trying to reduce
the latency, we should aim to reduce the bandwidth. For this reason this
commit introduces the ability to disable the nagle algorithm on the
socket after a successful SYNC.

This feature is off by default because the delay can be up to 40
milliseconds with normally configured Linux kernels.
TCP_NODELAY after SYNC: changes to the implementation.
LASTSAVE is a "random" command.
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