Zend_Db allows an 'adapterNamespace' to be specified. This would allow us to remove core/Db.php (Piwik_Db::factory) and go back to using Zend_Db::factory.
Changes: - config/global.ini.php and config/config.ini.php.sample - plugins/Installation/Controller.php - core/Piwik.php
Remove: - core/Db.php
Update script: - add adapterNamespace to config/config.ini.php - alternative is to set this at runtime
Let's not change this for now. The extra abstraction may help others in porting Piwik to other databases (e.g., Postgresql).