Now always checking in the DB if we saw the visitor earlier. The cookie also becomes much smaller. 
 Renamed the setting enable_detect_unique_visitor_using_settings now called trust_visitors_cookies as it is different logic, and should only be enabled in intranet where IP is same for all users.
 This will also help getting 1st party cookie implemented Refs #409

git-svn-id: http://dev.piwik.org/svn/trunk@3634 59fd770c-687e-43c8-a1e3-f5a4ff64c105