SELECT command mapping not honored in transactions

[slorello89]

Hey @NickCraver @mgravell 👋
Follow on to #1988 - originally fixed by #2023 looks like there's a case where if you remove select from the command map and try to run a transaction with ad-hoc commands, it will have a write failure. As it turns out when the RedisTransaction enqueues a message it checks to see if it's unknown/eval/evalsha and creates a select message and it enqueues that afterwards. I'll open up a PR in a couple minutest to address - figured I'd open an issue for tracking.