parse non-ascci filenames

failing spec, not sure how to fix :/

when I remove the rescue in `def element` I get:
```
Mail::ContentTypeElement can not parse |application/msword; name="Êëèêîâàÿ_ðåêëàìà.doc"|
       Reason was: Only able to parse up to application/msword; name="Ê
```

@jeremy @bf4
When in doubt, check the RFCs. Single quotes are used to separate charset information from values.

`[^a]+` style regexp are usually clearer to people than relying on non-greedy qualifiers.

Looks like this is an underlying bug in the parser, not in the field value fetcher. Regexping the field value is a huge red flag.