Option to choose how to login user

[SDKiller]

Now login is done both by username and email.

Would be nice to define in config (or settings) how exactly you want to log in user (for example - only by email).

Current way may be left as default to keep BC.

[bizley]

What are the benefits of this? Both are unique and you can provide either in the same field. The only thing I can think of is with username allowed to be log with potential hacker already knows half the required data.

[SDKiller]

Say, forum is part of the application where login by email was used for a long time and we do not want to encourage new practice.

[bizley]

Ok, this can be added as an option when inherited email address #107 issue is ready.