Allow SPOP from Lua scripts

[itamarhaber]

The existing R flag appears to be sufficient and there's no apparent reason why the command should be blocked.

Ref: #2139

[ramonsnir]

I think it has to do with the randomness of the item selection?

[itamarhaber]

@ramonsnir the R flag means "random command" and should thus remain. The s flag blocks the command's usage from Lua scripts entirely, and that's not what the other random commands use.

Prior to v3.2 random commands were not allowed in Lua scripts after writes, but you could always call them before (i.e in "read-only" mode). From v3.2 and onwards, we have redis.replicate_commands() that allows calling random commands even after writes.

[antirez]

Thanks @itamarhaber, yep looks like an error. Backporting to 3.2.