If sqlImport.errors is not writable, old import errors will be provided to the user

If the files/civicrm/upload/sqlImport.errors is not writable by the web user (e.g. www-data), CiviCRM will silently fail to overwrite sqlImport.errors with the errors from the most recent attempted import. Therefore, when the user is given the option to download import errors, they will download the last-written import errors instead of the actual errors from their most recent import.

Instead of grabbing the old copy of sqlImport.errors, CiviCRM should report that sqlImport.errors is not writable and advise the user on how to get that fixed.