Change Details

Right now the signup form uses the `users` API to check username availability; this does not allow username control extensions to influence the process so the user might not get any warning about an invalid username until after posting the form. It also does not support a "this is how the username will actually look like" response (e.g. automatic sentence casing). There should be an API (a new one or a part of `createaccount`) which does this via AuthManager.