Bugfix: Login Bug by multiple Installations on the same Domain

The Bug is showing if you have multiple Installations on the same domain.
Loging in htmly1/ as Kanti and you're automatically logged in at htmly2/.

the Bug is fixed by simply replacing all
$_SESSION['user']
by
$_SESSION[config("site.url")]['user']
and replacing
session_destroy();
by
unset($_SESSION[config("site.url")]);