I'm beginning to wonder if we shouldn't make this a universal file backup checker where you have an option for the URI and filename and the module puts all of the pieces together and makes the checks. Just make the default file wp-config.php and the script will do the rest, but also giving you the flexibility to look for other file backups as well..
That won't work right. You need the original extension to make the rest work and not every file will be php. For the checks dont include the original extension, strip it like so: '.'.join(filename.split('.')[:-1]) or filename[:filename.rindex('.')].