visitor differentiation based on a custom variable #3309

solution for the issue discussed here: http://forum.piwik.org/read.php?2,87411

problem summary: visits are assigned to the last customer to log in to the site using piwik tracking when two or more customers are using the same computer during the lifetime of a piwik cookie

solution summary: I replaced the uuid based on browser info and timestamp with one based on the same browser info, a session id passed to the Tracker object at instantiation and a date string (to force a new visit if the session id did not expire after date change).

Keywords: visit session cookie

Attachment: add custom session id to identify unique visits based on who is logged in the site
custom_sessions.diff

please review :)

Thanks for the patch, nice idea, but probably we won't include this as a feature.