redis-cli --stat, stolen from redis-tools.

Redis-tools is a connection of tools no longer mantained that was
intented as a way to economically make sense of Redis in the pre-vmware
sponsorship era. However there was a nice redis-stat utility, this
commit imports one of the functionalities of this tool here in redis-cli
as it seems to be pretty useful.

Usage: redis-cli --stat

The output is similar to vmstat in the format, but with Redis specific
stuff of course.

From the point of view of the monitored instance, only INFO is used in
order to grab data.
Test: obuf-limits test false positive removed.

Fixes #621.
Update config.c

Fix bug in configGetCommand function: get correct masterauth value.
Allow SELECT while loading the DB.

Fixes issue #1024.
Transactions: use the propagate() API to propagate MULTI.

The behavior is the same, but the code is now cleaner and uses the
proper interface instead of dealing directly with AOF/replication
functions.
Transactions: use discardTransaction() in EXEC implementation.
Transactions: propagate MULTI/EXEC only when needed.

MULTI/EXEC is now propagated to the AOF / Slaves only once we encounter
the first command that is not a read-only one inside the transaction.

The old behavior was to always propagate an empty MULTI/EXEC block when
the transaction was composed just of read only commands, or even
completely empty. This created two problems:

1) It's a bandwidth waste in the replication link and a space waste
   inside the AOF file.

2) We used to always increment server.dirty to force the propagation of
   the EXEC command, resulting into triggering RDB saves more often
   than needed.

Note: even read-only commands may also trigger writes that will be
propagated, when we access a key that is found expired and Redis will
synthesize a DEL operation. However there is no need for this to stay
inside the transaction itself, but only to be ordered.

So for instance something like:

    MULTI
    GET foo
    SET key zap
    EXEC

May be propagated into:

    DEL foo
    MULTI
    SET key zap
    EXEC

While the DEL is outside the transaction, the commands are delivered in
the right order and it is not possible for other commands to be inserted
between DEL and MULTI.
Flag PUBLISH as read-only in the command table.
Test: new functions to capture and analyze the replication stream.
Test: Restore DB back to 9 after testing MULTI/EXEC with DB 5.
Test: test replication of MULTI/EXEC.
Test: read_from_replication_stream, workaround for 2.6
DEBUG set-active-expire added.

We need the ability to disable the activeExpireCycle() (active
expired key collection) call for testing purposes.
Test: verify that lazy-expire works.
Better DEBUG error message when num of arguments is wrong.
Test: regression test for issue #1026.
EXPIRE should not resurrect keys. Issue #1026.
Extended SET command implemented (issue #931).
Test: Extended SET tests.
Support for case unsensitive SET options.