Auto-converted audio files should not be backed up/restored in "all files" scenario

We should try to detect if changed/removed/added audio files are merely due to an automatic conversion (wavs to 16 bit, mp3s to wavs, oggs to wavs) and exclude them from the backup/restore.

Not exactly a bug in the strictest sense, it's behaving as designed, but it's not really what we want in this case.