Avoid the same user to login more time

[Valerio Pachera]

Hi all, I noticed that is possible to login with the same user from
more than one client and also on the server.

I tried to log in with the same user and open rekonq on both of them.
On the second terminal, rekonk was complaining about the last session
was not closed fine.
But this happens because the browser is already opened in the other terminal.

Is there a way to avoid a user to login more than one time?