Send back an exception or error code if user already exists.

[imaginator]

Creating the same user twice always returns "OK"

curl https://tellmo.buddycloud.com/api/account -X POST -H "Content-Type: application/json" -H "Accept: application/json" -d "{ \"username\": \"user2@tellmo.buddycloud.com\", \"password\": \"12345678\", \"email\": \"azeem.akram@devbatch.com\" }"        

If we try to use this command with an already used "username" it still returns OK. Should it not return any Error or Exception that username already exist?

[jamestait]

An HTTP 409 response might be appropriate, but would enable a malicious user to enumerate the usernames on a given domain.