username check command

[ornicar]

Occasionally we're getting emails asking us why a certain username cannot be registered. Sometimes it's obvious and easy to reply, while some others it's some obscure lamename hit that's really hard to identify.
Could we have a cli command that checks if a username can be registered and if no, returns exactly why?
Ie
- Already registered
- Registered in the past (we can't share this explicitly but helps formulating an answer)
- Unacceptable name: matches [exact lamename match]
It could also be useful for troubleshooting lamename excessive FPs/testing