Refs #2902

 * Provider plugin does not do dns reverse lookup when ip was anonimized since it does not work and is slow to fail
 * Changed recommended "IP Anonymization" from 1 byte to 2 bytes as per recos in http://piwik.org/privacy/
 * Now IP is anonmized only after IP Exclude was tested. All code should use the anonymized IP. If there is a need later to access the non original raw IP, we can add this in the code, but for now there is no such use case

Refs #1823
 * For Geoip it means that the plugin will only have access to the anonymized IP. 
  * It would be nice if we could still guess the country at least from the anonymized IP. But I suppose that the IP ranges are not evenly distributed between countries and several countries would share the same IP ranges (with the last 2 bytes removed)... 
  * If guessing country or region, is not possible from the anonymized IP, it is an acceptable tradeoff that GeoIP does not work when IP anonymization is enabled, since it's the condition to respect visitors privacy. Once confirmed, we could document this in the Anonymize IP UI tooltip.


git-svn-id: http://dev.piwik.org/svn/trunk@5775 59fd770c-687e-43c8-a1e3-f5a4ff64c105