This class can manage user access sessions providing some security features.
It verifies whethers the IP address and the browser identification (user agent) are not different from those used when the session is created. Otherwise, the session is flagged as invalid. An exception is opened for users accessing the site via AOL, due to the rotating proxy problem.
It also provides functions for setting, getting, removing and checking the existance of individual session variables.
The session variables can be referred using dots for separating the names of indexes of sessions variables stored in multi-dimensional associative arrays, like for instance, "config.ip" instead for $_SESSION["config"]["ip"].