By default PHP error messages and printDebug() output are displayed to all users accessing the admin or widgets. This can provide server information to malicious users. A new option should be added to config.ini.php to disable all error output to the browser. Additionally it would be useful to set this option separately for admin and non-admin users.
Currently the only way to disable printDebug() is by setting
$GLOBALS['PIWIK_TRACKER_DEBUG'] = false
Instead of adding a new config value, another option would be to default PIWIK_TRACKER_DEBUG to false and only set it to true if an admin is logged in.
By default PHP error output is enabled with the display_errors option. The default should be to suppress PHP error output and only enable it for admin users.
Since we're in development mode, I've deferred this request to post-1.0.
In the meantime, you can add that one-liner to a bootstrap.php file in your root piwik folder (which isn't overwritten by an update).
I can't think of an expected use case where Piwik would throw errors and this wouldn't be a bug. In all cases, errors should not be thrown but should be caught and properly handled. Closing as won't fix. If such error show up, please create a ticket and we will ensure that they are handled with a human readable error message, or don't make the Piwik UI or tracking fail.
Is there no way for me to mark these recent updates as spam?
I've removed that spam...