* Adding automatic crontab task triggered from Tracking requests on piwik.php.
 * Define max frequency in config file, default to 1 try each hour.
 * Will not run if 'Browser archiving' is disabled, as it means the cron is already setup, and it will run scheduled tasks.
 * Note that Scheduled tasks only do not necessarily trigger archiving. The user might still experience slow loading time if he loads Piwik after a long absence. 
We could consider writing a scheduled tasks that triggers archiving daily for each website 

git-svn-id: http://dev.piwik.org/svn/trunk@2767 59fd770c-687e-43c8-a1e3-f5a4ff64c105