This commit changes what provided by PR #3315 (merged) in order to
let the user specify the log level as a string.

The define could be also used, but when this happens, they must be
decoupled from the defines in the Redis core, like in the other part of
the Redis modules implementations, so that a switch statement (or a
function) remaps between the two, otherwise we are no longer free to
change the internal Redis defines.

It's more natural to call the last entry added as "last", the original
commet got me confused until I actually read the code.

Most of the time to check the last element is the way to go, however
there are patterns where the contrary is the best choice. Zig-zag
scanning implemented in this commmit always checks the obvious element
first (the last added -- think at a loop where the last element
allocated gets freed again and again), and continues checking one
element in the head and one in the tail.

Thanks to @dvisrky that fixed the original implementation of the
function and proposed zig zag scanning.

Optimized autoMemoryFreed loop

fix: config set list-max-ziplist-size didn't support negative values

This bug most experienced effect was an inability of Redis to
reconfigure back old masters to slaves after they are reachable again
after a failover. This was due to failing to reset the count of the
pending commands properly, so the master appeared fovever down.

Was introduced in Redis 3.2 new Sentinel connection sharing feature
which is a lot more complex than the 3.0 code, but more scalable.

Many thanks to people reporting the issue, and especially to
@sskorgal for investigating the issue in depth.

Hopefully closes #3285.

I recently introduced populating the autocomplete help array with the
COMMAND command if available. However this was performed before parsing
the arguments, defaulting to instance 6379. After the connection is
performed it remains stable.

The effect is that if there is an instance running on port 6339,
whatever port you specify is ignored and 6379 is connected to instead.
The right port will be selected only after a reconnection.

Close #3314.

Reference issue #3218.

Checking the code I can't find a reason why the original RESTORE
code was so opinionated about restoring only the current version. The
code in to `rdb.c` appears to be capable as always to restore data from
older versions of Redis, and the only places where it is needed the
current version in order to correctly restore data, is while loading the
opcodes, not the values itself as it happens in the case of RESTORE.

For the above reasons, this commit enables RESTORE to accept older
versions of values payloads.

CLIENT error message was out of date

fix georadius returns multiple replies

Comment format fixed + local var modified from camel case to underscore
separators as Redis code base normally does (camel case is mostly used
for global symbols like structure names, function names, global vars,
...).

fix crash in BITFIELD GET on non existing key or wrong type see #3259

Sentinel: fix check when can't send the command to the promoted slave

fix mistake in comment in object.c

Fix modules intro typos.

bitcount bug:return non-zero value when start > end (both negative)

Allow non-interactive execution of install_server

BSDs don't have -ldl

Related to #3293.

Related to #3293.

We need to be free to shuffle fields or add more fields in a structure
without breaking code.

Related to issue #3293.

Now that modules receive RedisModuleString objects on loading, they are
allowed to call the String API, so the context must be released
correctly.

Related to #3293.

Related to PR #3293.

Allow passing arguments to modules on load.

fix some compiler warnings

Fix MODULE UNLOAD crash and/or wrong error message.