So, replacing:
```
if infoname == "upload_date":
    value = self.hyphenate_date(value)
```
with:
```
xattr.set( filename, 'user.dublincore.date', self.hyphenate_date(info_dict.get('upload_date')) )
```

That makes the code a lot less readable.

It also removes the "upload_date" from the `xattr_mapping` dict.

I think for clarity and simplicity, I'm going to leave it as it is.