Related to #4498.

- when redis-cli is running in a TTY - always enable command history
buffering, regardless if history file path can be successfully
determined

Fix #3665.

The function in its initial form, and after the fixes for the PSYNC2
bugs, required code duplication in multiple spots. This commit modifies
it in order to always compute the script name independently, and to
return the SDS of the SHA of the body: this way it can be used in all
the places, including for SCRIPT LOAD, without duplicating the code to
create the Lua function name. Note that this requires to re-compute the
body SHA1 in the case of EVAL seeing a script for the first time, but
this should not change scripting performance in any way because new
scripts definition is a rare event happening the first time a script is
seen, and the SHA1 computation is anyway not a very slow process against
the typical Redis script and compared to the actua Lua byte compiling of
the body.

Note that the function used to assert() if a duplicated script was
loaded, however actually now two times over three, we want the function
to handle duplicated scripts just fine: this happens in SCRIPT LOAD and
in RDB AUX "lua" loading. Moreover the assert was not defending against
some obvious failure mode, so now the function always tests against
already defined functions at start.

The block is already inside if (allow_dup).

Unfortunately, as outlined by @soloestoy in #4505, "lua" AUX RDB field
loading in case of duplicated script was still broken. This commit fixes
this problem and also a memory leak introduced by the past commit.

Note that now we have a regression test able to duplicate the issue, so
this commit was actually tested against the regression. The original PR
also had a valid fix, but I prefer to hide the details of scripting.c
outside scripting.c, and later "SCRIPT LOAD" should also be able to use
the function luaCreateFunction() instead of redoing the work.

With PSYNC2 to force a full SYNC in tests is hard. With this new DEBUG
subcommand we just need to call it and then CLIENT KILL TYPE master in
the slave.

In the case of slaves loading the RDB from master, or in other similar
cases, the script is already defined, and the function registering the
script should not fail in the assert() call.

Related to #4483. As suggested by @soloestoy, we can retrieve the SHA1
from the body. Given that in the new implementation using AUX fields we
ended copying around a lot to create new objects and strings, extremize
such concept and trade CPU for space inside the RDB file.

See #4483. This is needed because luaCreateFunction() is now called
from RDB loading code outside a client context.

This is currently needed in order to fix #4483, but this can be
useful in other contexts, so maybe later we may want to remove the
conditionals and always save/load scripts.

Note that we are using the "lua" AUX field here, in order to guarantee
backward compatibility of the RDB file. The unknown AUX fields must be
discarded by past versions of Redis.

Doing the following ended with a broken server.executable:

1. Start Redis with src/redis-server
2. Send CONFIG SET DIR /tmp/
3. Send DEBUG RESTART

At this point we called execve with an argv[0] that is no longer related
to the new path. So after the restart the absolute path of the
executable is recomputed in the wrong way. With this fix we pass the
absolute path already computed as argv[0].

Splitting the popularity in half actually just needs decrementing the
counter because the counter is logarithmic.

Firstly, use access time to replace the decreas time of LFU.
For function LFUDecrAndReturn,
it should only try to get decremented counter,
not update LFU fields, we will update it in an explicit way.
And we will times halve the counter according to the times of
elapsed time than server.lfu_decay_time.
Everytime a key is accessed, we should update the LFU
including update access time, and increment the counter after
call function LFUDecrAndReturn.
If a key is overwritten, the LFU should be also updated.
Then we can use `OBJECT freq` command to get a key's frequence,
and LFUDecrAndReturn should be called in `OBJECT freq` command
in case of the key has not been accessed for a long time,
because we update the access time only when the key is read or
overwritten.

Signed-off-by: NBo Cai <charpty@gmail.com>

Signed-off-by: NBo Cai <charpty@gmail.com>