More succinct header output for PHP errors
i18n for PHP error output in the console
Forcibly return true from our custom error handler when doing AJAX requests so extensions such as Xdebug don't break things
Alter the header in db.php file so it's not chosen as the first plugin by `get_plugins()`. Fixes the "Invalid header" issue.
Merge branch 'develop'
Mark as 2.5.6