Update from 2.6.9 to 2.6.10.
UPGRADE URGENCY: MODERATE, this release contains many non-critical fixes
and many small improvements.
* [BUGFIX] redis-cli --rdb, fixed when the server sends newlines to ping.
* [BUGFIX] redis-cli, minor fixes on connection handling, prompt.
* [BUGFIX] Slow log: don't log EXEC, just executed commands.
* [BUGFIX] On failed shutdown don't try again and again compulsively.
* [BUGFIX] Fix build on sunos without backtrace().
* [BUGFIX] UNSUBSCRIBE and PUNSUBSCRIBE: always provide a reply (see 742e580)
* [BUGFIX] Lua struct library was broken, upgraded.
* [BUGFIX] Fix a bug in srandmemberWithCountCommand() with count argument.
* [BUGFIX] Test: disable clients timeout to prevent issues on slow systems.
* [BUGFIX] Sentinel: don't advertise the promoted slave as master too early.
* [IMPROVED] Whitelist SIGUSR1, see http://redis.io/topics/signals.
* [IMPROVED] Simpler to understand redis-cli --bigkeys output.
* [IMPROVED] Test now works with tclsh > 8.5.
* [IMPROVED] Added option to turn of the Nagle algorithm in slave socket.
* [IMPROVED] Optionally use SO_KEEPALIVE to detect dead peers.