Fix semantics of Lua calls to SELECT.

Lua scripts are executed in the context of the currently selected
database (as selected by the caller of the script).

However Lua scripts are also free to use the SELECT command in order to
affect other DBs. When SELECT is called frm Lua, the old behavior, before
this commit, was to automatically set the Lua caller selected DB to the
last DB selected by Lua. See for example the following sequence of
commands:

    SELECT 0
    SET x 10
    EVAL "redis.call('select','1')" 0
    SET x 20

Before this commit after the execution of this sequence of commands,
we'll have x=10 in DB 0, and x=20 in DB 1.

Because of the problem above, there was a bug affecting replication of
Lua scripts, because of the actual implementation of replication. It was
possible to fix the implementation of Lua scripts in order to fix the
issue, but looking closely, the bug is the consequence of the behavior
of Lua ability to set the caller's DB.

Under the old semantics, a script selecting a different DB, has no simple
ways to restore the state and select back the previously selected DB.
Moreover the script auhtor must remember that the restore is needed,
otherwise the new commands executed by the caller, will be executed in
the context of a different DB.

So this commit fixes both the replication issue, and this hard-to-use
semantics, by removing the ability of Lua, after the script execution,
to force the caller to switch to the DB selected by the Lua script.

The new behavior of the previous sequence of commadns is to just set
X=20 in DB 0. However Lua scripts are still capable of writing / reading
from different DBs if needed.

WARNING: This is a semantical change that will break programs that are
conceived to select the client selected DB via Lua scripts.

This fixes issue #1811.
Scripting: regression test for issue #1811.
Add SIGINT handler to cli --intrinsic-latency

If we run a long latency session and want to Ctrl-C out of it,
it's nice to still get the summary output at the end.
add missing signal.h include
Add correct exit value to failed tests

(Note from @antirez: modified to apply to 2.8)
Sentinel framework new layout back ported 2.8.

Functionally the same, but makes cherry picking simpler.
redis.tcl: return I/O error message when peer closes connection.
Test: tcl client, unset deferred var on close.
Test: Tcl client initial support for automatic reconnection.
Test: use higher level redis.tcl proc to read replies.
Sentinel test: add manual failover test.
Sentinel: handle SRI_PROMOTED flag correctly.

Lack of check of the SRI_PROMOTED flag caused Sentienl to act with the
promoted slave turned into a master during failover like if it was a
normal instance.

Normally this problem was not apparent because during real failovers the
old master is down so the bugged code path was not entered, however with
manual failovers via the SENTINEL FAILOVER command, the problem was
easily triggered.

This commit prevents promoted slaves from getting reconfigured, moreover
we now explicitly check that during a failover the slave turning into a
master is the one we selected for promotion and not a different one.
Sentinel: send hello messages ASAP after config change.

Eventual configuration convergence is guaranteed by our periodic hello
messages to all the instances, however when there are important notices
to share, better make a phone call. With this commit we force an hello
message to other Sentinal and Redis instances within the next 100
milliseconds of a config update, which is practically better than
waiting a few seconds.
Sentinel test: unit 02, avoid some time related false positives.
Sentinel test: tolerate larger delays in init tests.
Jemalloc update script added.
Jemalloc updated to 3.6.0.

Not a single bug in about 3 months, and our previous version was
too old (3.2.0).
sdscatfmt() added to SDS library.

sdscatprintf() relies on printf() family libc functions and is sometimes
too slow in critical code paths. sdscatfmt() is an alternative which is:

1) Far less capable.
2) Format specifier uncompatible.
3) Faster.

It is suitable to be used in those speed critical code paths such as
CLIENT LIST output generation.
Added new sdscatfmt() %u and %U format specifiers.

This commit also fixes a bug in the implementation of sdscatfmt()
resulting from stale references to the SDS string header after
sdsMakeRoomFor() calls.
Use sdscatfmt() in getClientInfoString() to make it faster.